Adapted from Bon Appetit
1 sheet frozen puff pastry (half of 17.3 ounce package), thawed or 8 ounces homemade puff pastry
4 ounces prosciutto
2 tablespoons chopped fresh basil
3/4 cup freshly grated Gruyère cheese, packed
1 egg, beaten to blend
Place puff pastry on work surface, lightly dusted with flour. Cut in half, forming two 9 1/2 x 4 3/4 inch rectangles. Arrange half of prosciutto on one rectangle, leaving an empty border of 1/2 inch along one side. Sprinkle with half the basil, then half the cheese. Brush border with beaten egg. Starting at end opposite of border, roll up like a jelly roll. Press to seal long edges. Repeat with second pastry sheet. Refrigerate at least 3 hours and up to 2 days.
Preheat oven to 400º. Line two large baking sheets with parchment paper. Cut rolls into 1/2 inch slices. Arrange on baking sheets leaving a 1 inch space between rounds. Bake 16 minutes, till golden brown. It works best baking one sheet at a time. Cool slightly on racks. Serve warm. Makes 30.