Blackberry Poppy Seed Cake

This blackberry poppy seed cake recipe features an easy, moist cake packed full of poppy seeds, with alternating layers of vibrant purple blackberry basil jam and a lightly sweetened mascarpone cream frosting.

This cake is a celebration of late summer flavors, particularly blackberry and basil, which are growing in abundance in my garden (the basil, thankfully) and neighborhood at this time of year.

It's topped with a delicate caramel sauce drip and a crown of late summer fruit.

I've been wanting to make a jam filled cake recipe like this ever since seeing a scroll-stopping cross section of a similar cake on Instagram from the delight inducing Seattle cake shop, Deep Sea Sugar & Salt.

Their version used a black currant blackberry jam and cream cheese frosting, but I had a vat of mascarpone in the fridge again, and a small forest of basil growing in our raised garden beds out front.

I went over the top and added a caramel sauce drip and some seasonal late summer fruit as decoration. I loved the visual drama of deep purple blackberries, figs, and blueberries, and thought it played well with the golden glow of the caramel sauce.

The glorious combination of sweet, acidic blackberries and creamy mascarpone is one I discovered a few summers ago. I put together a honey blackberry mascarpone ice cream during my race to use up a 5 pound container of mascarpone cheese.

I also made this chocolate coffee mascarpone tart, and this lemon mascarpone ice cream with a red currant swirl. There's also grilled peaches with honey and mascarpone. See how nicely mascarpone plays with so many other flavors?

The poppy seed cake is my adaptation of a well loved poppy seed loaf cake published in the NY Times. It's filled to the brim with poppy seeds soaked in warm milk to tenderize their tough outer shell and release extra flavor. It's delicate, moist and has a slightly nutty flavor. The textural crunch is a nice foil for the creamy mascarpone.

The blackberry basil jam is an easy recipe that pairs two classic summer flavors into a deliciously sweet and sharp combination. The spicy flavor of Genovese Basil tempers the jam's sweetness and keeps it all from being cloying.

And there's the mascarpone, a delightfully adaptable ingredient with a wide range of uses that can swing either sweet or savory. Here I've used it in a lightly sweetened mascarpone cream frosting to which I've added a bit of vanilla and almond extract. Whipped with heavy cream, it thickens beautifully, creating the delight sometimes known as chantilly mascarpone.

Mascarpone icing is wonderfully easy to spread on the cake layers, pipe as a dam to keep the jam from escaping, and cover the cake's exterior with a minimal naked look.

I dripped a whisper thin layer of caramel sauce over the cake to add a golden touch and nice notes of deeply toasted sugar. The fresh fruit piled atop the cake echoes the notes of late summer present in the flavors, and provides a simple, minimal decoration. The bonus? Edible cake decorations!

Ingredients

POPPY SEED CAKE

Poppy Seeds - Yes, this is a significant amount of poppy seeds! The recipe calls for 100 grams (¾ cup) which is the amount you see reflected in the photos here. You're welcome to reduce the amount by half if the texture is too seedy for you.

I recommend buying poppy seeds in bulk, as they're more affordable than the small jars in the grocery store. For the cake, soak the poppy seeds in hot milk to soften their outer coating and help release additional flavor when baked.

Whole milk - You can substitute with milk alternatives here if desired. The milk is warmed to soak the poppy seeds.

All purpose flour provides structure in the cake.

Baking powder - for leavening the cake and adding volume. With no strong acid in the ingredients, baking powder provides both the base and acid needed for the cake to rise.

Kosher salt - for added flavor.

Unsalted butter - The butter should be cubed and at room temperature.

Granulated sugar - for sweetness, tenderness, and moisture.

Eggs - as a binder to provide structure to the cake, as well as adding fat and flavor.

Vanilla extract, almond extract, and lemon zest add flavor and compliment the poppy seeds.

BLACKBERRY BASIL JAM

Fresh blackberries - You can substitute frozen blackberries here if needed. Just thaw them fully before cooking.

Fresh basil leaves - I have Genovese basil, also known as sweet basil, growing in my garden. I picked enough leaves to measure ½ ounce, which is ¾ cup of loosely packed leaves.

You must use fresh leaves in this recipe. Do not substitute with dried basil. Other basil varieties will work as well. They'll each impart their own unique flavor.

Lemon juice - Lemon juice improves the taste and lowers the pH of the jam. This helps the pectin set as it releases from the cooked and sweetened fruit. Using either fresh or bottled lemon juice is fine for this purpose.

Granulated sugar - Sugar sweetens the jam and helps the natural pectin to set. This is a fairly low sugar jam, so I don't recommend reducing the amount any further.

For help telling when your jam is finished cooking, refer to this post. You can keep this blackberry jam, well sealed, in the refrigerator for up to a month.

Please consult an expert source on canning and food preservation if you wish to can this (or any) jam.

MASCARPONE CREAM FROSTING

Mascarpone cheese - The mascarpone provides the main flavor in this frosting recipe. It's important that you use it chilled here, directly from the fridge.

Here in the US, you can usually source an 8 ounce tub of mascarpone in the cheese section of the dairy aisle at your local grocery store. If you can't find mascarpone, you might substitute this creme fraiche buttercream recipe.

Heavy whipping cream - Also needs to be chilled, directly from the fridge.

Powdered sugar - Powdered sugar provides sweetness and a bit of thickening power.

Vanilla extract and almond extract, for a boost in flavor.

CARAMEL SAUCE

Granulated sugar and water are heated in a heavy saucepan until fully dissolved and golden brown in color. They form the base of the caramel sauce.

Heavy whipping cream - Cream provides the rich, smooth texture to the caramel sauce. Warming the cream before adding it to the hot sugar mixture will help reduce the possibility that the sugar will seize.

Unsalted butter - For extra richness and smooth mouthfeel.

Vanilla extract and Kosher salt, for flavor.

Blackberry liqueur - A few teaspoons of blackberry liqueur (crème de mûre) is an optional addition. It provides a subtle flavor of blackberry to the caramel sauce. You could also add crème de cassis, which is made from blackcurrants.

Frequently Asked Questions

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