For the cupcakes: Preheat the oven to 350 degrees F. Line one 12-cup standard muffin tin with paper cupcake liners.
In a small bowl, whisk the flour, ground graham crackers, baking powder and salt. Set aside.
In a stand mixer fitted with the paddle attachment, beat the butter and brown sugar on medium speed until combined. Increase the speed to medium-high and continue to beat, stopping once or twice to scrape down the sides of the bowl, until light and fluffy, 3 to 5 minutes. Add the eggs and vanilla and beat until combined. Add the flour mixture and milk, alternating, starting and ending with the flour mixture, until just combined.
Divide the batter between the muffin cups, filling each about two-thirds full. Bake until golden brown, or a toothpick inserted in the center comes out clean and the top springs back to the touch, about 25 minutes. Cool in the tin 5 minutes, and then transfer to a wire rack to cool completely.
For the filling: While the cupcakes cool, prepare the filling: Combine the chocolate, cream and corn syrup in a medium bowl and microwave in 30-second intervals on high, stirring, until smooth. Set aside until cooled and thickened slightly, about 30 minutes.
For the meringue frosting: Bring 1 inch of water to a simmer in a saucepan that can hold a heatproof stand mixer's bowl above the water. Combine the egg whites, granulated sugar and cream of tartar in the stand mixer bowl. Set the bowl above the simmering water and whisk until the sugar is dissolved and the egg whites are warm to the touch, turn white and are beginning to get fluffy. Transfer the bowl to the stand mixer, fitted with a whisk attachment, and whip on high speed until the meringue is cooled, fluffy and very thick. Beat in the vanilla.
To assemble: Place the chocolate filling in a pastry bag or re-sealable plastic bag fitted with a small round tip (about 1/8-inch diameter) and snip the end. Pierce the center of each cupcake with the pastry tip and gently squeeze in the chocolate filling until it begins to come out of the top of the cupcake. Repeat with the remaining cupcakes.
Pipe or swirl the meringue frosting onto each cupcake. If desired, brown the meringue with a kitchen torch or place briefly under the broiler. Garnish with a chocolate square.
Recipe courtesy of Food Network Kitchen