Make These Ooey, Gooey Grilled S'Mores Doughnuts

Ingredients

• 1 1/2 cups unsweetened cocoa powder
• 1 1/2 cups firmly packed brown sugar
• pinch of salt
• 2 cups half-and-half
• 1 1/2 teaspoons unsalted butter
• 8 marshmallows or 32 mini marshmallows
• 1/2 teaspoon pure vanilla extract
• 6 glazed doughnuts
• Cooking spray for doughnuts