Preheat your oven to 350 degrees F. Grease 2 10-inch or 3 9-inch cake pans with nonstick cooking spray. Place a parchment circle in the bottom of each pan and lightly spray that with nonstick cooking spray.
In a large bowl, add the 12 tablespoons butter, 4 large eggs, 2 large egg yolks, 1 cup granulated sugar, and 1 tablespoon vanilla extract. Beat on medium/high speed until it reaches the ribbon stage, about 5 minutes. Ribbon stage is when the mixture appears pale, fluffy, and when you pull the beater up, the batter will leave a trail that resembles a ribbon.
In a small bowl, whisk together the 4 tablespoons dutch processed cocoa powder and 1/2 cup hot water.
In a microwave-safe bowl, add the chopped 3/4 cup semi-sweet baking chocolate. Place in the microwave and microwave in 30-second intervals until completely smooth and melted.
Whisk the melted baking chocolate into the cocoa powder/water mixture until combined.
Add your chocolate mixture into the butter/egg mixture and beat until combined. Scrape down the sides of the bowl.
In the bowl that add the cocoa mixture, add the 1/2 cup plain yogurt and 1/2 cup whole milkWhisk until combined.
In a medium sized bowl, sift in your 1 3/4 cups all-purpose flour, 1 1/2 teaspoons baking soda, and 1/2 teaspoon salt.
Alternately add the flour and milk/yogurt mixture to the butter/egg mixture starting and ending with flour. Mix in each addition until combined and scrape down the sides of the bowl before adding the next.
Divide the batter into the prepared pans.
Place in the preheated oven for about 30 minutes if you using the 10-inch pans and begin checking the 9-inch pans at 20 minutes. Insert a toothpick in the center of the cake. If it comes out clean or with moist crumbs, it's done. If there's wet batter, let it bake longer.
Let the cakes cool for 10 minutes in the pan and turn out onto cooling racks to cool completely.