Preheat your oven to 350°F (175°C) and grease a 13x18 jelly roll pan.

In a mixing bowl, whisk together melted butter, whole milk, sour cream, and granulated sugar until smooth.

Add in the eggs and vanilla extract; beat until fully incorporated.

Sift together the flour, cocoa powder, baking soda, and salt into the wet mixture and fold gently.

Pour the batter into the prepared pan and bake for 20 minutes, or until a toothpick comes out clean.

Let the cake cool in the pan for about 10 minutes before preparing the frosting.

Cream together peanut butter and unsalted butter until smooth, then add powdered sugar until light and spreadable.

Spread the peanut butter frosting over the cooled cake evenly.

In a saucepan, melt butter, whole milk, corn syrup, and vanilla, then mix in chopped dark chocolate until blended.

Blend in powdered sugar until the glaze is glossy, then pour over the frosted cake.

Allow the cake to cool for at least 30 minutes before serving.