Preheat the oven to 350 degrees. Grease a 6-inch round cake pan and a 6-inch square cake pan with non-stick spray. Line the bottoms with parchment paper and set aside.
In a medium bowl whisk together the flour, cocoa powder, baking powder, baking soda and salt. Then set aside.
1 ½ cups (187 g) all-purpose flour, spooned and leveled, 2 tablespoon (10 g) Dutch process cocoa powder, 1 teaspoon baking powder, ¼ teaspoon baking soda, ¼ teaspoon salt
To a large bowl add the softened, unsalted butter and granulated sugar. Cream together with an electric mixer on high speed until fluffy, 1-2 minutes. (You can also use a stand mixer fit with a paddle attachment.) 7 tablespoon (98 g) unsalted butter, softened, 1 cup (200 g) granulated white sugar
Then add in the eggs and vanilla. Mix on medium speed until pale in color and smooth, 1-2 minutes.
2 eggs, at room temperature, 1 teaspoon vanilla
Alternate adding the dry ingredients and the buttermilk to the butter mixture. Mix on low speed until all is just combined and the batter is smooth. Scrape down the sides of the bowl as necessary.
⅔ cup (158 ml) buttermilk, at room temprature
Lastly, fold in the red gel food coloring just until combined.
2 teaspoon red gel food coloring
Divide the cake batter evenly between the prepared pans. Bake the cakes for 26-29 minutes. Let the cakes cool in the pans for 2 minutes, then transfer them to wire racks to cool completely.