Oreo Upside-Down Sheet Cake | epicuricloud (Tina Verrelli)

Ingredients

• non-stick baking spray with flour
• 1 package Oreo Double Stuff cookies (divided)
• 1/3 cup +2 tablespoons unsalted butter (softened, divided)
• 1/3 cup cocoa powder
• 1/2 cup semi-sweet chocolate chips
• 1/2 teaspoon instant espresso powder (optional)
• 1/3 cup boiling water
• 1/2 cup buttermilk (regular milk fine too!)
• 1/2 + 1/3 cup (113g) all-purpose flour
• 1/2 teaspoon salt
• 1/2 teaspoon baking soda
• 1/2 cup granulated sugar
• 1/2 cup light brown sugar, packed
• 2 teaspoons vanilla extract
• 3 large eggs (room temperature)
• 2 tablespoons unsalted butter (softened)
• 1 cup confectioners' (powdered) sugar
• 2 tablespoons milk (room temperature)