1. Combine 3/4 cup butter, egg yolks and vanilla extract in large bowl. Beat at low speed with electric mixer until blended. Set aside cocoa packet from Mix. Gradually add cake mix. Blend well.

2. Divide dough in half. Add cocoa packet and remaining 1 tablespoon butter to half the dough. Knead until well blended and chocolate colored.

3. Roll out yellow dough between two pieces of waxed paper into a 6" square. Repeat with chocolate dough. Remove top pieces of waxed paper from yellow and chocolate doughs. Cut each square into twelve 1/2" wide strips.

4. To assemble, place one strip chocolate dough on plastic wrap. Brush edge with beaten egg. PLace one strip yellow dough next to chocolate dough. Brush edge with egg. Repeat with a second chocolate strip, egg and a second yellow strip to make first row. Brush top of row with egg. Prepare second row by stacking strips on first row, alternating yellow over chocolate strips. Brush edge and top of each strip with egg. Repeat for third row to complete one checkerboard bar. Repeat with remaining strips to make second bar. Cover with plastic wrap. Refrigerate 1 hour or until firm enough to slice.

5. Preheat oven to 350'F. Grease baking sheets.

6. Cut checkerboard bars into 1/4" slices. Place 2" apart on greased baking sheets. Bake at 350'F. for 7-9 minutes or until edges are light golden brown. Cool 1 minute on baking sheets. Remove to cooling racks. Cool completely. Store in airtight containers.