Place the metal tray, tea towel and pyrex bowl in the middle of the sunlight from the mirrors, so it warms up. This should be in a position on a table that is safe. out of reach of children, out of the wind, with space to put another tray, oven mitts down. Adjust the mirrors to reflect the sunlight to the middle of the metal tray, it works best upside down with a mirror underneath it. Otherwise a bluestone or concrete tile. Place the cupcake cooker in the middle of the mirror array, careful to keep the pyrex bowl clear of the mirrors. The pyrex can get hot enough to crack any mirror it touches.