Mix the brown sugar and butter coating: In a medium bowl, stir together the packed brown sugar and melted butter until you have a thick, glossy mixture. It should look like a loose caramel. If it seems too stiff, warm it briefly or add a teaspoon of water to loosen.
Coat the dough pieces: Add the biscuit pieces to the brown sugar–butter mixture and gently toss until every piece is coated. Take your time to get the sugar mixture distributed; this is what creates the sticky, caramel-like texture inside each packet.
Fill and seal the foil packets: Divide the coated dough pieces among the prepared foil squares, creating small mounds in the center of each piece of foil. Bring the sides of the foil up and over the dough and crimp the edges together to seal, forming loose but closed packets. Leave a little space inside each packet so steam can circulate.
