Preheat the oven to 350°F. Generously spray a 12-cup muffin tin with cooking spray, or line with cupcake liners.
In a gallon-sized plastic bag, combine the granulated sugar and cinnamon. Seal and shake to mix well.
Open the biscuit cans and spread all 16 biscuits on a cutting board. Using kitchen scissors, cut each biscuit into 8 pieces (cut in half, then quarters, then eighths).
Drop 8-10 biscuit pieces into the cinnamon sugar bag. Seal and shake until completely coated. Place exactly 8 coated pieces into each muffin cup. Repeat until all pieces are coated and distributed.
In a microwave-safe bowl, melt the butter in 30-second intervals. Stir in the brown sugar until smooth and well combined.
Drizzle about 2 tablespoons of the butter-brown sugar mixture over each muffin cup, allowing it to seep between the biscuit pieces.
Bake for 15-20 minutes, until the tops are golden brown and slightly puffed. Check at the 15-minute mark through the oven window.
While baking, make the glaze by whisking together the powdered sugar and 1 tablespoon of milk. Add more milk by the teaspoon until desired drizzling consistency is reached.
Remove from oven immediately and let cool in the pan for 5 minutes. Run a butter knife around edges if needed, then transfer to a wire cooling rack.
While still warm, drizzle the powdered sugar glaze over each portion using a fork. Let the glaze set slightly before serving.