Preheat the oven to 350 degrees. Grease a 9 inch springform pan and line the bottom with parchment paper. Set aside.
In a small bowl, whisk together the all purpose flour, cocoa powder, baking powder, baking soda and salt. Then set aside the dry ingredients.
1 cup (125 g) all-purpose flour, spooned and leveled, 6 tablespoon (30 g) Dutch process cocoa powder, ¾ teaspoon baking powder, ⅛ teaspoon baking soda, ¼ teaspoon salt
In a large bowl, cream the sugar and the butter together with an electric mixer on high speed until fluffy, about 1-2 minutes. (You can also use a stand mixer fit with a paddle attachment.)
1 cup (200 g) granulated white sugar, 6 tablespoon (84 g) unsalted butter, softened
Then add in the egg, egg yolk, and vanilla and mix on medium-high speed until smooth and pale in color, about 1-2 minutes. Scrape the sides of the bowl with a rubber spatula as needed.
1 egg, at room temperature, 1 egg yolk, at room temperature, ½ teaspoon vanilla
Add in the flour mixture and the buttermilk to the wet ingredients a little at a time, mixing on low speed until all is combined and the batter is smooth.
⅔ cup (160 ml) buttermilk, at room temperature
Add in the hot coffee and mix on low speed until combined.
¼ cup (60 ml) hot coffee
Pour the cake batter into the preapred pan. Then pour the cream cheese filling over top and spread it in an even layer with a mini offset spatula.
Bake the cake for 38-42 minutes. The center will have a jiggle still.
After baking, let it cool on a wire rack for 45 minutes. Then transfer the cake to the fridge to cool for 2 hours.