Step 1: Prepare the Tart Crust: In a mixing bowl, combine wheat flour, powdered sugar, and salt. Add the softened butter and mix until the mixture resembles thick crumbs. Insert egg yolk until batter is combined. If necessary, add a teaspoon of cold water to help unite the mass. Press the dough at the bottom and sides of the tart molds. Prick the bottom with a fork to avoid bubbles. Refrigerate the crust for approximately 30 minutes.
Step 2: Preheat the Oven: Preheat your oven to 350°F (175°C).
Step 3: Bake the Tart Crusts: Remove the crusts from the refrigerator and bake them in the preheated oven for about 15-20 minutes or until they are slightly golden brown. Remove and let cool.
Step 4: Make the Filling: In a mixing bowl, beat together the granulated sugar, yuzu juice, lime juice, eggs, and grated zests until smooth and well combined.
Step 5: Fill the Tarts: Pour the filling mixture into the cooled tart crusts, filling them up to about 3/4 of their capacity.
Step 6: Bake the Tarts: Bake in the oven for an additional 15-20 minutes or until the filling is firm and slightly jiggly in the center. Remove from oven and let cool completely.
Step 7: Serve: Once cooled, garnish with whipped cream and lime slices or yuzu if desired. Serve cold or at room temperature.