In a small bowl combine the flour, sugar, and cardamom. Mix to combine. Add the cold butter and incorporate the flour using your fingers by squeezing the butter in between your index and thumb as if you were making pie dough or biscuits. The mixture should be mealy and resemble wet sand. Add the sliced almonds at the end (to help them keep their shape) and mix to combine. Set aside until ready to top the cake.
For the blackberry apple crumb cake
Preheat the oven to 350°F. Grease and line a 9” x 3” round cake pan. The cake bakes up high, so you’ll want to use a 3” deep cake pan!
While the oven preheats, spread the almonds onto a baking tray and toast the nuts while the oven preheats, about 5-7 minutes or until fragrant. Let cool slightly and then grind in a food processor or chop using a knife if you’re not lazy like me.
In a stand mixer fitted with the paddle attachment, cream the softened butter and granulated sugar on medium speed until pale and fluffy, about 3-4 minutes.
In a small bowl, combine the flour, toasted ground almonds, baking powder, baking soda and kosher salt. Mix so all the ingredients are evenly dispersed.
Once the butter and sugar are light and fluffy, decrease the speed to low and gradually add the eggs one at a time ensuring each egg is incorporated before adding the next. Add the vanilla extract and increase speed to medium and mix until light and fluffy. Scrape down the sides of the bowl and the paddle attachment.
Next, we will alternate between the dry and wet ingredients. Add ⅓ of the flour mixture and mix until just incorporated. Add ½ of the buttermilk and mix until incorporated. Repeat. Pour cake batter into prepared cake pan and smooth top with an offset spatula so it is even and level.
Top the cake with the sliced apples and then the blackberries ensuring they are evenly dispersed. Top with the almond streusel crumb topping.
Bake for 55-65 minutes or until a cake tester comes out clean, rotating halfway. Let cool in cake pan on top of cooling rack. Top with confectioners’ sugar and serve.