Heat oven to 350ºF. Line 2 cupcake pans with 24 liners.

Sift together the flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer or a medium mixing bowl, beat the sugar and butter until light and fluffy. Beat in the vanilla and 1/2 cup of milk until just blended. Add half the flour mixture and mix on low speed until combined. Add the remaining milk; mix until combined. Add the remaining flour and mix until just combined.

In a second bowl, add the egg whites and cream of tarter. Beat with an electric mixer on high until the egg whites are glossy and form stiff peak when the mixer is lifted. Gently fold the egg whites into the batter, one quarter at a time.

Divide the batter between the prepared cupcake pans. Bake 20-25 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Remove from the oven and let cool completely.

Fill a pot with 1inch of water; bring to a simmer. Combine the egg whites, sugar, cream of tartar, and salt in a heatproof bowl. Set the bowl over the pot and cook for 3-4 minutes or until the mixture reaches 160ºF, whisking constantly. Remove from heat and whisk on high for 7-10 minutes, or until the frosting holds stiff peaks.

Heat broiler on high.

Use a paring knife to cut a cone out of the center of each cupcake. Spoon 1 teaspoon of lemon curd into the hole, then replace the cake that you removed.

Spoon or pipe 1 tablespoon of frosting onto the top of each cupcake. Sprinkle with graham cracker crumbs and place on a baking sheet.

Broil for 1-2 minutes, or until graham cracker crumbs and marshmallow frosting are golden and toasted, but not burned (keep a close eye on them!)