Black Cocoa Brownie with Dark Chocolate Bailey's German Buttercream

Ingredients

• 113g cold unsalted butter
• 225g dark chocolate, coarsely chopped
• 50g Black cocoa, or extra dutched cocoa
• 140g all-purpose flour
• 1/2 tsp baking powder
• 3/4 tsp salt
• 4 large eggs, at room temperature
• 120g neutral oil
• 300g sugar
• 100g brown sugar
• 2 tsp vanilla
• 110g granulated sugar
• 12g corn starch
• 1 egg, at room temperature
• 1 egg yolk, at room temperature
• 1/2 tsp salt
• 1 tsp vanilla bean paste
• 190g Bailey’s or Irish Cream
• 340g unsalted butter, at room temperature
• 180g dark chocolate, melted and then cooled.