1. Make a meringue In a large bowl, beat egg white on high speed until stiff peaks form. Gradually add in the sugar, and whisk until the meringue looks glossy.
2. Line a baking tray with parchment paper. With a pastry bag, pipe this meringue into a disc shape (a bit smaller than the tart, see picture) and transfer the baking sheet to the oven. Bake it for about 60min. Remove from the oven and let it to cool to room temperature on a wire rack. Set aside.
3. Make a tart Process flour, almond powder, sugar, butter and egg yolk in a food processor for a few seconds until the mixture becomes crumbly : do not process too much as the dough should be crumbly.
4. Transfer the dough onto a work surface. Gather it into a ball shape of dough with hands. Gently flatten the ball into a disc shape and wrap it in plastic wrap. Refrigerate for at least 30min.
5. Roll the dough : Put a plastic wrap covering on your work surface, place the dough on it. Then cover with another piece of plastic wrap. Let it sit for a few min to soften slightly. Roll the dough out into circle bigger than your tart mold. Then place gently into your tart mold (or ring). Using a sharp knife, trim the edges of the pastry to fit the tart pan. Prick bottom and side of tart thoroughly with a fork. Put it in the refrigerator until firm (about 30min).
6. Preheat oven to 170C degree. Line the firm tart shell with parchment paper or aluminum foil and fill it with pie weights or dried beans.
7. Bake for 15min and then remove the parchment and weights. Continue baking for another 8 to 10 min at 180C degree or until the dough is just beginning to brown lightly. Cool on a wire rack until needed.
8. Put the tart together Place the disc shaped meringue on the tart base (if the meringue is too big, just cut it off).
9. In a small saucepan, add heavy cream and chocolate and heat over medium-low heat, stir until it is hot but not boiling. Remove from the heat and gently stir and melt the chocolate with remaining heat until smooth and creamy in texture.
10. Pour the chocolate filling over the meringue in the crust. Place in the fridge to cool for a few hours.