Into 10-inch skillet, place ground beef, onion, salt and pepper. Cook over medium-high heat until beef is browned; drain. Stir in cumin, chili powder and tomato sauce. Reduce heat to low; cook 5 minutes longer.
Heat oven to 400°F. Place silicone baking mat on cookie sheet with sides.
On baking mat, unroll dough into 1 large rectangle; press perforations and edges to seal. Using 4-inch round cutter, cut out 8 dough rounds.
To make each empanada, place about 2 tablespoons beef mixture onto center of each dough round. Using pastry brush (or fingers), gently brush edge of each round with beaten egg white. Fold dough round in half to cover filling; press edge together to seal. (To make decorative edge, fold dough over itself so that it forms a rope look.) Lightly brush tops of empanadas with beaten egg yolk.
Bake 10 to 12 minute or until golden brown. Serve warm.