Generously spray a 10-inch bundt pan with non-stick spray.
Wrap a Reese's cup into a biscuit half like a dumpling. Pinch the seams to make sure that the Reese's cup is covered by the biscuit dough. You may need to smoosh and spread the biscuit dough a little into a flat circle about 2-inches in diameter to wrap the Reese's cup.
Arrange the dough balls in the prepared pan.
In a medium bowl, whisk together the butter and brown sugar.
Drizzle it evenly over the dough balls.
Bake at 325 degrees for 40-50 minutes, or until the edges are golden brown, and when you press toward the center, it should feel 'set'. I use the end of a wooden spoon to press lightly toward the center of the bundt to check for doneness. You don't want it to feel doughy.
Remove from heat, and cool in pan for 10 minutes. Run a knife or small rubber spatula along the edges to loosen the bread.
Invert onto a serving platter. Do not wait longer than 10 minutes to invert, or the bread will stick to the pan.
Prepare peanut butter glaze.
In a medium bowl, whisk together powdered sugar, melted peanut butter, and 1/4 c. milk until smooth, adding additional milk as needed.
Drizzle evenly over monkey bread.
Sprinkle with chopped Reese's cups, if desired, for garnish.
Individual servings reheat easily in the microwave for 20-30 seconds!