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All Lavender is edible but most of them don't taste that great. Grow English Lavender (Lavandula angustifolia) if you plan to cook with it.
Lavender Cookies
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1 cup sugar
2 eggs
3 cups flour
4 tablespoons fresh lavender flowers, crushed
Cream together butter, sugar and eggs. Mix in the flour and lavender flowers. Spoon onto a cookie sheet. Bake about 15 minutes @ 350 degrees F. (You might as well double the batch right now because you know in your heart that you want to...)