When making a foil bag, the size of the piece of foil you start out with varies based on the desired final size of your foil bag. For a more heavy-duty bag, two pieces of foil can be layered one on top of the other. Start by folding the foil in half, giving it a little crease. This crease is the base of the bag. Next, fold the sides, creasing along the edge with each fold. Each side should be folded at least three times to make sure you to get a seal inside the bag. Turn the bag around, and repeat the folds on the opposite side. Now, you have a foil bag with an opening on the top. This can be filled with rosemary, potatoes, carrots … anything you’d like.
To use your foil bag, open it up, and carefully put the vegetables inside. Hold up the bag, shimmy the vegetables down, and seal the bag shut by folding the foil over another three times, creasing the foil with each fold. And with that, the veggies are ready for roasting. A good seal with create a steam bag that will help infuse flavour and speed up cooking.