Crust

1. In a medium mixing bowl, place the butter and sugar. Beat until lighter in color and texture. Add the egg, vanilla, and salt and continue mixing until uniform, scraping down the sides as needed. Add the flour, mixing until the dough comes together and begins to gather in the bowl. A food processor can also be used to speed up the process, if available.
2. Remove dough and shape into a cylinder. Wrap in plastic wrap and refrigerate for a minimum of 30 minutes.
3. Preheat oven to 400 degrees F (205 degrees C).
4. Unwrap dough and slice cylinder into 6 even pieces. On a lightly floured surface, roll out each slice into a circle 2-inches larger than the tart pan. Gently place dough into pan, pressing it along the edges. If necessary, additional dough can be used to cover up cracks or tears. Using a rolling pin, roll it along the top of the pan to cut off excess dough. Puncture a couple dozen holes into the bottom of the tart using a fork; this will prevent the dough from rising.
5. Bake for 15-20 minutes, or until they are dry in appearance and touch. Cool to room temperature.

Chocolate Filling

1. Place chopped chocolate in a bowl. Set aside.
2. On the stovetop or in the microwave, heat the cream until near boiling. Pour over the chopped chocolate and allow to sit for 5 minutes to melt the chocolate. Stir until smooth.
3. Divide chocolate filling evenly between the cooled tart shells, using an offset spatula to smooth the top of each tart.

Marshmallow Topping

1. Wipe a large bowl with a paper towel soaked in a small amount of lemon juice or vinegar to remove traces of grease. Add egg whites and sugar and, over a double boiler, whisk constantly over hot water until the sugar dissolves. When rubbed between your fingers, the egg whites should feel hot and smooth (approximately a temperature of 140 degrees F/60 degrees C). This will generally take 3-8 minutes, depending on the temperature of the water.
2. Using a mixer, whip the egg whites until thick, glossy peaks form. This may take anywhere from 8-10 minutes. Beat in the vanilla extract.
3. Using a pastry bag, pipe topping over each tart. The tarts may be covered partially (as shown) or fully covered. Alternatively, an offset spatula can be used to spread topping over the tarts.
4. For a toasted look, use a kitchen torch (or a full-sized blow torch, as I did) to add the toasted look to the topping. I recommend practicing on leftover topping before starting on the tarts. Alternatively, an oven set to broil can be used to toast the topping. This is a little less precise, but will also yield a toasted appearance.
5. Store and serve at room temperature. The marshmallow topping may “weep” slightly on the second day, but it does not affect the flavor or texture of the tarts.