Creating your Nectarine Frangipane Tart is easy when you follow these steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Make Tart Shell: In a mixing bowl, combine the flour and sugar. Add the cold butter and mix until it resembles coarse crumbs. Stir in the egg yolk and water until a dough forms. Chill for 30 minutes.
3. Roll Out Dough: On a lightly floured surface, roll out the chilled dough to fit a 9-inch tart pan. Press it into the pan and trim any excess dough.
4. Blind Bake: Place parchment paper over the dough and fill with pie weights or beans. Bake for 15 minutes, then remove the weights and bake for an additional 5-10 minutes until lightly golden. Set aside to cool.
5. Prepare Frangipane Filling: In a bowl, beat the softened butter and sugar until creamy. Add the eggs, one at a time, mixing well after each addition. Stir in the almond flour, all-purpose flour, almond extract, and vanilla extract until combined.
6. Assemble Tart: Spread the frangipane filling evenly over the cooled tart shell. Arrange the sliced nectarines on top in a decorative pattern. Sprinkle with brown sugar and sliced almonds if desired.
7. Bake Tart: Bake in the preheated oven for 30-35 minutes, or until the frangipane is set and golden brown.
8. Cool: Remove from the oven and let cool in the pan for 15-20 minutes before transferring to a serving platter.
9. Optional Glaze: For a glossy finish, you can brush the top with warmed apricot jam or honey.

By following these steps, you will create a stunning Nectarine Frangipane Tart that is sure to impress!