Roll out pasta frolla dough and line a 12-inch tart mold. Chill for 10 minutes. Preheat oven to 325°F. Line tart with parchment and beans, then bake for 20 minutes. Cool and remove shell.
In a bowl, combine cream, egg yolks, whole egg, lemon juice and zest, sugar, and vanilla. Cook in a double boiler while whisking until foam rises, then falls. Add butter and softened gelatin sheet.
Continue whisking until thickened. Cool over an ice bath, then pour into tart shell. Refrigerate until set. Whip egg whites with sugar until stiff peaks form. Pipe onto tart, then torch to golden brown before serving.
