Pumpkin leaves are, indeed, edible. In many parts of the world, including Asia and Africa, they are a regular part of the diet when available. They can be steamed like spinach, sauteed in some olive oil with garlic and salt, or used in stir frys. The taste is similar to a mixture of green beans, asparagus, broccoli, and spinach.
Pumpkin leaves can be eaten cooked or raw, although the raw leaves have a rough, prickly texture that disappear when cooked. For the best results, choose young leaves while they are still tender. If you wait until your pumpkins are huge, the leaves will be tougher although they are still fine if cooked long enough to become tender.
Pumpkin leaves are high in calcium and also are a good source of vitamins A, B6, C, protein, riboflavin, niacin, thiamin, folate, iron, magnesium, phosphorus, potassium, and manganese.
For a simple side dish, take 1 lb of rinsed pumpkin leaves, 1 tablespoon of cooking oil, 1 tsp salt and 2 to 3 cloves chopped garlic. Sautee the leaves in the oil and salt for about five minutes or until tender. Add garlic and continue to cook until the garlic begins to brown. Serve immediately over rice. Alternatively, sautee a chopped onion and some garlic in oil until the onion is tender and transparent, add the pumpkin leaves and continue to sautee. Add a chopped tomato at the end and cook.
You can also fry the pumpkin blossoms in some butter or oil for a tasty treat.