Preheat oven to 400°F. Beat butter and sugar until well combined (about 2 minutes). Beat in egg whites, one at a time, 4 minutes after each addition. Add flour until combined.
Place nonstick baking mat on top of a baking sheet and place your stencil on the mat. Using a spatula spread a *thin* layer of batter over the stencil. Lift stencil off carefully. Repeat, making more leaves, spacing evenly on the baking mat.
Bake for 4 minutes. Using spatula, drape leaves over a rolling pin to cool.
Finishing: Melt chocolate chips and place in a Ziploc baggie. Cut corner of bag and squeeze chocolate onto cookies in the pattern of veins on a leaf. Let set until chocolate is dry.