Candied lemon peel rests on a pillow of lemon mousse in this delicate, delectable tart.
Preheat oven to 375 degrees. On a lightly floured surface, roll the dough 1/8 inch thick. Fit dough into a 7-inch fluted tart shell, letting it fall naturally into the corners and being careful not to stretch the dough. With your fingers or a rolling pin, trim dough so that it is flush with top edge of tart shell. Prick the tart shell all over with the tines of a fork. Chill until firm, at least 45 minutes.
Line dough with parchment paper and fill with dried beans or lentils. Transfer to oven and bake until tart shell begins to color, about 20 minutes. Carefully remove the dried beans and parchment and return to the oven and bake until the tart shell becomes a deep golden color, about 15 to 20 minutes more. Cool completely on a cooling rack.
In a small saucepan, soften the gelatin in the water. Add the lemon juice and stir over a very low flame just until gelatin is thoroughly dissolved. Remove from the heat and let cool completely over a bowl of ice water. This mixture must be completely cooled before being added to the egg whites.
In a medium bowl, whip the heavy cream to stiff peaks. Set aside.
In the bowl of an electric mixer, beat the egg whites until soft peaks form on medium speed. Increase the speed to medium-high and gradually add the sugar. Beat until stiff peaks form. Decrease speed again and slowly add the gelatin mixture. Remove bowl from mixer and gently fold in the whipped cream and grated lemon rind, being careful not to deflate the meringue.
Mound the mousse in the baked tart shell and chill for at least 4 hours.
Make the candied lemon peel: Using a vegetable peeler or a sharp paring knife, remove the rind from the lemon, avoiding the bitter white pith. Slice into thin strips.
Blanch the strips in boiling water and shock in ice water. Repeat process twice. Drain lemon strips and reserve.
In a small saucepan, combine water and sugar. Bring to a slow boil, lower the heat to a simmer, add the lemon strips; cook for about 40 minutes, until the lemon peel is translucent.
Remove the peels from the syrup and let cool on a wire rack. Let sit until hardened, about 30 minutes.
Garnish the chilled tart with candied lemon peel and serve.