You only need three ingredients to make this St. Paddy's app: puff pastry, pesto and an egg. Roll out a sheet of thawed puff pastry into a 12-by-14-inch rectangle on a floured surface and cut a 1/2-inch-thick strip from one long side (for the stems). Spread pesto on the rectangle, then roll both long sides toward the middle until they meet (see below). Cut the log into 1/2-inch-thick slices and pinch the bottom of each slice to form a heart shape. Arrange three hearts together on a parchment-lined baking sheet to create a shamrock shape, using beaten egg to "glue" the sides together. Cut the reserved strip of dough into stems; lightly press onto the shamrocks and brush the stems with more beaten egg. Bake at 400 degrees F, about 15 minutes.