1 cup butter or margarine, softened
1 cup granulated sugar
1 egg
1 tablespoon vanilla extract
2 ounces white chocolate, coarsely chopped
1/4 cup semisweet chocolate chips
2 1/2 to 3 cups all-purpose flour
1 1/2 teaspoons baking powder
1/4 teaspoon salt

Cream butter; gradually add sugar, beating at medium speed of electric mixer until light and fluffy. Add egg and vanilla extract; beat well. Divide mixture in half, putting halves in separate bowls. Set aside.

Place white chocolate in top of double boiler; bring water to a boil. Reduce heat to low; cook until chocolate melts. Remove from heat and let cool slightly.

Place chocolate chips in top of double boiler; bring water to a boil. Reduce heat to low; cook until chocolate melts. Remove from heat and let cool slightly.

Stir white chocolate into one portion of creamed mixture; stir semisweet chocolate into remaining portion of creamed mixture.

Combine flour, baking powder, and salt. Stir 1 1/4 to 1 1/2 cups flour mixture into each portion of chocolate mixture, stirring well. Cover and refrigerate both portions.

On floured wax paper, roll each half of dough into a 15- x 8-inch rectangle. Invert white dough carefully onto dark dough; peel wax paper from white dough. Tightly roll dough jellyroll fashion, starting at long end, and peeling wax paper from dough as you roll. Cover and chill 1 hour.

Slice dough about 1/4 inch thick, and place on ungreased cookie sheets. Bake at 350 degrees F for 10 to 12 minutes. Remove to wire rack to cool.

Yields about 5 dozen.