01 -
In a food processor, combine the light brown sugar, pecans, and cinnamon. Pulse until the nuts are coarsely chopped but not pulverized—you want some texture. Transfer about 3/4 cup of this mixture to a small bowl and stir in the chopped chocolate. This will be your filling. Set it aside. To the remaining mixture in the food processor, add the cake flour, unsweetened cocoa powder, cold cubed butter, and espresso powder. Pulse several times until the mixture becomes crumbly with small butter pieces throughout. This creates your topping. Set it aside while you prepare the cake batter.
02 -
Position a rack in the center of your oven and preheat to 325°F (165°C). Thoroughly butter the bottom and sides of a 9-inch springform pan or a 9×9-inch square baking pan. For extra insurance against sticking, spray the buttered pan with cooking spray or line with parchment paper. Set aside.
03 -
In a medium bowl, sift together the all-purpose flour, baking powder, baking soda, and salt. This ensures there are no lumps and that the leavening agents are evenly distributed. Set this dry mixture aside while you prepare the wet ingredients.
04 -
In the bowl of an electric mixer fitted with the paddle attachment, beat the softened butter at medium-high speed for about 1 minute until creamy and lightened in color. Gradually add the granulated sugar and increase to high speed, beating until the mixture is light and fluffy, about 2 minutes. This creates air pockets that help the cake rise. Add the eggs one at a time, beating well after each addition and scraping down the sides of the bowl as needed to ensure everything is evenly incorporated. Beat in the vanilla extract until just combined.
05 -
Reduce the mixer speed to low. Add the dry ingredients and liquid ingredients in alternating batches, beginning and ending with the dry ingredients: first add 1/3 of the flour mixture and mix until just incorporated, then add all of the buttermilk. Add another 1/3 of the flour mixture, followed by all of the Greek yogurt. Finish with the remaining flour mixture, mixing just until combined. Be careful not to overmix at this stage, which can develop the gluten in the flour and result in a tough cake.
06 -
Scrape half of the batter into your prepared pan and smooth the top with a spatula. Evenly sprinkle the reserved chocolate-pecan filling over this layer, leaving a small border around the edges. This helps prevent the filling from seeping out during baking. Carefully spread the remaining batter over the filling layer, being gentle so you don't disturb the filling too much. Smooth the top. Finally, evenly sprinkle the cocoa-pecan topping mixture over the entire surface of the cake.
07 -
Place the pan in your preheated oven and bake for 50 to 60 minutes, or until a toothpick inserted into the center of the cake comes out clean or with just a few moist crumbs attached. Begin checking at around 50 minutes, as oven temperatures can vary. The cake is done when it's set in the center and the edges have begun to pull away slightly from the sides of the pan.
08 -
Allow the cake to cool in the pan set on a wire rack for 10 minutes. If using a springform pan, carefully release and remove the sides of the pan. Let the cake cool completely on the wire rack before serving, which takes about 2 hours. This cooling time allows the flavors to develop and the texture to set properly. Once cooled, slice and serve. The cake can be stored at room temperature, covered, for up to 3 days.