Milk Bar Pie

Ingredients

• Oat Cookie Crust
• Nonstick vegetable oil spray
• 9 tablespoons (1 stick plus 1 tablespoon) unsalted butter, room temperature, divided
• 5 1/2 tablespoons (packed) golden brown sugar, divided
• 2 tablespoons sugar
• 1 large egg
• 3/4 cup plus 2 tablespoons old-fashioned oats
• 1/2 cup all purpose flour
• 1/8 teaspoon baking powder
• 1/8 teaspoon baking soda
• 1/4 teaspoon (generous) salt

Filling

• 3/4 cup sugar
• 1/2 cup (packed) golden brown sugar
• 1 tablespoon nonfat dry milk powder
• 1/4 teaspoon salt
• 1/2 cup (1 stick) unsalted butter, melted, cooled slightly
• 6 1/2 tablespoons heavy whipping cream
• 4 large egg yolks
• 1 teaspoon vanilla extract
• Powdered sugar (for dusting)