Marbled Mocha Tart

1/4 cup butter, softened
3/4 cup granulated sugar
1 teaspoon vanilla extract
1/2 cup sifted Dutch process cocoa
1 cup all-purpose flour
6 ounces chopped white chocolate
6 ounces chopped semisweet chocolate
1 cup whipping cream
1 tablespoon instant espresso powder

Preheat oven to 375°F (190°C). In food processor, combine butter, sugar and vanilla and process until smooth. Add cocoa powder and process to blend. Add flour and pulse until mixture begins to hold together. Press mixture onto bottom and sides of 10-inch tart pan with removable bottom. Pierce bottom all over with fork. Place in freezer 10 minutes. Bake 15 minutes. Set aside to cool. Place the white and semisweet chocolate in separate bowls. In saucepan bring cream to gentle boil. Stir in espresso powder. Pour half of hot espresso cream into each bowl. Stir until smooth. Fill tart shell with the semisweet chocolate mixture. On top of the dark chocolate filling, pour five separate pools of white chocolate mixture. Pull tip of knife through fillings to marbleize. Refrigerate until set. Makes 12 servings.