For the pastry, mix together the flour, sugar, cinnamon, and salt in a large bowl until combined. Grate the frozen butter over the bowl, stirring it every 30 seconds to help coat the individual shards of butter in the flour mixture. Make a well in the center of the mixture and add the egg yolks and 1/3 cup of the water. Stir the well with a fork until a dough starts to form. Add the remaining water around the well and begin to knead the entire mixture together until a cohesive dough forms, adding another tablespoon or two of water if necessary to get the dough to come together. Separate the dough into two separate equally-sized balls, cover each with plastic wrap, and refrigerate for 30 minutes.

For the 9-inch tart pan, roll out the dough until it is 1/4 inch thick and forms an 11-inch square and transfer to a well-greased and lightly floured -inch tart pan. Press the dough into the pan and trim off any excess. Cover with plastic wrap and place in the freezer for 30 minutes. If you’d like to make mini-tarts, roll out the dough to the same specification but use a inch circular cookie cutter to cut a circle out of the dough. Place the circle in the well of a well-greased and lightly floured muffin pan, pressing the dough into the corners of the well. Repeat until each well has a crust. Cover the pan with plastic wrap and place in the freezer for 30 minutes.

Preheat the oven to 375 degrees Fahrenheit. Remove the plastic wrap from the crusts and prick all over with a fork. Pre-bake the 9-inch tart crust for 13 minutes and the mini tart crusts for 7 minutes. Remove and allow to cool slightly while you prepare the custard.

For the custard, place a large casserole dish 3/4 full of water on the bottom rack of the oven. Strain the almonds and discard the soaking liquid. Puree the soaked almonds with the milk, creme fraiche, sugar, honey, lemon juice, and lemon zest at high speed until completely smooth.

Empty the mixture into small saucepan and place over medium low heat, stirring every 3 minutes.

Once the mixture is hot but not boiling, remove it from the heat and ladle some of the milk mixture into a medium bowl with the egg yolks, whisking them together rapidly. Continue until you’ve added about half the milk mixture to the yolks, then empty the yolk mixture back into the saucepan and place it back over medium low heat. Sprinkle in the flour and whisk vigorously until smooth. Continue cooking until the custard has thickened slightly, about 4 minutes, stirring every minute.

Remove from heat and fill the 9-inch tart pan about 3/4 full of filling, use a ladle to fill each mini tart about 3/4 full of the filling. Place the pans in the oven, and bake the 9-inch tart until the edges are set but the middle is slightly jiggly, about 12 to 15 minutes. Bake the mini tarts for about 8 to 10 minutes. Allow the tarts to cool for 30 minutes before attempting to remove them from their respective pans. Garnish by sprinkling the top with slivered almonds and powdered sugar. Serve immediately.