To build a cardboard box reflector oven:

Get a sturdy cardboard box (liquor boxes are sturdy; 6 half-gallon size is good). It must fit over the pan (9x13 or 10x15) being used and have about a 1-inch clearance all around. This allows for air flow and even heat for baking.

Line inside with heavy duty foil — SHINY SIDE SHOWING. Line it first from end to end; then side to side. (Form foil over outside of box so it slides into bottom of box easily. The fewer creases in the foil, the better the reflection.)

Use tin can (approximately 29-32 oz; #2%) as a chimney for charcoal starting. Remove ends and puncture holes around one end (bottom) of chimney can.

Use foil on the ground for base of oven — SHINY SIDE UP. Clear away bumables on ground so soil is clean. Set on soil or concrete, NEVER on wood or asphalt surfaces. (Watch out! The concrete will get hot!)

Fill chimney can with one fire starter and right number of charcoal briquets (each briquet = 40 degrees FULLY LIT — be sure to count them). Read recipe for heat needed.

Start charcoal 20-30 minutes before baking for “ready” coals. When coals are fully gray, they are “ready”.

Spread hot charcoal with tongs in an area about the size of a baking pan (9x13 pans work well).

Use 6 ounce metal juice or vegetable cans to support baking pan at four corners.

Put box oven upside down over baking pan and hot charcoal, propping up one long edge about 1/2 inch for ventilation, away from any wind blowing (leeward side). Follow baking time directions for item being baked. When checking for doneness, raise box slowly straight up (don’t spill the heat), peek, then replace if more time is needed.