Microwave half-and-half, butter, and chopped bittersweet chocolate in a microwave-safe bowl at HIGH 2 minutes or until chocolate melts. Stir until smooth. Stir together sugar, cocoa, flour, and salt in a medium bowl. Stir in eggs, egg yolks, and melted chocolate mixture. Use immediately, or pour filling into a 1-qt. jar; let cool. Store filling in refrigerator up to 7 days. (Mixture will thicken as it chills.)
TO MAKE HOT FUDGE PIE: Preheat oven to 350°. Fit 1 refrigerated piecrust into a lightly greased 9-inch deep-dish pie plate according to package directions; fold edges under, and crimp. Pour Hot Fudge Pie Filling into prepared crust; bake 45 minutes or until filling puffs, center is set, and top begins to crack around the edges. Cool 10 minutes before serving.
PACKAGE IN: Weck Tall 28.7-oz. Glass Jar ($4.50; westelm.com)