Grease and lightly flour a 10 1/2-inch tart or quiche pan. Set aside.
To prepare the crust, mix together the flour, powdered sugar, almond meal, and salt in a large bowl until blended.
Cut the butter into pea-sized pieces over the bowl, stirring to coat the pieces in the flour mixture. Use a dough scraper or pastry cutter to chop at the mixture in the bowl to cut the butter into even smaller pieces.
Empty the mixture into the bowl of a stand mixer fitted with the paddle attachment. Add the egg and vanilla extract. Mix at medium-low speed until they are just incorporated, taking care not to overwork the dough.
Roll out the dough on a lightly floured piece of parchment paper until it is 1/4-inch thick.
Flip the sheet over onto the tart pan and peel the parchment sheet off, leaving the dough on the pan.
Press the dough into the pan and trim excess dough to form the crust to the pan. Poke the crust all over with a fork to keep bubbles from forming. Cover with plastic wrap and place the crust in the freezer for one hour.
Preheat the oven to 375 degrees Fahrenheit.
Grease a sheet of aluminum foil and press the greased side snugly onto the crust, tucking it down over the edge of the tart pan to ensure all parts of the crust are completely covered and none are exposed.
Bake the crust for 30-40 minutes or until fragrant and lightly golden around the edges. Gently remove the tin foil and set the crust aside to cool while you prepare the white chocolate filling.
In the top of a double boiler over gently simmering water, mix together the white chocolate, cream, and peppermint extract. Continue stirring until the chocolate melts and the mixture is smooth.
Remove from heat and immediately pour into the prepared tart crust until full.
Allow the filling to set for 1 hour before arranging the sliced almonds on top of the tart. Sprinkle with the powdered sugar and serve.
Will keep covered in the refrigerator for up to four days.