To prepare dough, lightly spoon flour into dry measuring cups; level with a knife. Combine flour, 1/3 cup sugar, baking powder, and salt in a food processor; pulse to combine. Add butter and cream cheese; pulse 4 times or until mixture resembles coarse meal. With processor on, add 3 tablespoons milk through food chute, processing just until dough forms a ball. Press mixture gently into a 4-inch circle on plastic wrap; cover. Chill for 1 hour.
To prepare filling, wipe food processor clean with a paper towel. Combine 1/4 cup sugar and farmer's cheese in processor; process 1 minute or until well blended. Cover and chill. Combine 1 tablespoon milk and egg white in a small bowl; set aside.
Preheat oven to 425°.
Roll dough to a 1/8-inch thickness on a heavily floured surface; cut with a 3-inch biscuit cutter into 24 circles. Discard any remaining dough scraps. Spoon about 2 teaspoons cheese mixture onto half of each circle; place 2 pieces guava paste on cheese, leaving a 1/2-inch border. Brush egg mixture around edges of each circle. Fold dough over filling; press edges together with a fork or fingers to seal. Place empanadas on 2 baking sheets coated with cooking spray; brush tops of empanadas with remaining egg mixture.
To prepare topping, combine 3 tablespoons sugar and cinnamon in a small bowl; sprinkle sugar mixture evenly over empanadas. Bake at 425° for 10 minutes or until golden. Remove from oven; cool completely on a wire rack.