Halfway Squares

• ⅓ cup butter, cut in chunks
• 1 egg, separated
• ¼ cup

Preheat oven to 375°F.

For base: Process butter, egg yolk, granulated sugar and ¼ cup brown sugar on the steel blade for 45 seconds, until blended. Add flour, baking powder and vanilla extract. Process with several on/off pulses, until mixed. Press into sprayed 8-inch square pa