How to Make It
Sift together flour, pudding mix, baking powder, and 1/2 teaspoon salt in a medium bowl.
Scrape vanilla bean seeds from pod into bowl of a heavy-duty stand mixer fitted with the paddle attachment. Add butter and sugar, and beat on medium speed until pale and creamy, about 4 minutes. Add eggs, 1 at a time, beating until well combined after each addition. Reduce speed to low, and add flour mixture. Beat until combined, about 1 minute. Cover and chill 30 minutes.
Using plastic wrap, shape dough into a 2 1/2- x 10-inch log; wrap in plastic wrap, and freeze until firm, about 2 hours.
Preheat oven to 325°F. Remove and discard plastic wrap, and cut log into 1/2-inch-thick slices; place on a parchment paper–lined baking sheet, leaving 2 inches between cookies. Bake in preheated oven until just set on top and light golden brown on bottom, about 15 minutes, rotating baking sheet after 7 minutes. Cool completely on baking sheet, about 10 minutes.
Place chocolate in a heatproof bowl. Bring cream and corn syrup to a simmer in a small saucepan over medium, stirring constantly, until combined. Pour cream mixture over chocolate in bowl; season with a pinch of salt, and stir until smooth.
Bring corn syrup and sugar to a boil in a small saucepan over medium-high, stirring constantly, until sugar is dissolved and mixture is combined, 2 to 3 minutes. Cook, stirring often, until a candy thermometer registers 240°F, about 3 minutes. Beat egg white with a stand mixer fitted with the whisk attachment until frothy. Slowly pour hot corn syrup mixture into beaten egg white, and add 1/8 teaspoon salt. Beat until white, fluffy, and meringue holds a soft peak, about 2 minutes.
Using an offset spatula, frost half of top of each cookie with black frosting and the other half with white frosting. Let stand at room temperature until frostings are dry to the touch, about 1 hour. Arrange cookies in a single layer on a large rimmed baking sheet; wrap tightly with plastic wrap. Let cookies stand 8 hours or overnight. (Cookies are best after standing at least 24 hours.)