Creating a Nectarine Tart can be straightforward if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Prepare the Crust: In a mixing bowl, combine flour and granulated sugar. Add the diced butter and mix until the mixture resembles coarse crumbs.
3. Add Egg Yolk: Stir in the egg yolk and enough cold water to form a dough. Knead gently until smooth.
4. Chill the Dough: Wrap the dough in plastic wrap and refrigerate for 15-20 minutes.
5. Prepare the Filling: In another bowl, mix the sliced nectarines with brown sugar, vanilla extract, lemon juice, cornstarch, and cinnamon (if using).
6. Roll Out Dough: On a floured surface, roll out the chilled dough into a circle about ¼ inch thick.
7. Transfer to Tart Pan: Place the dough into a tart pan, pressing it gently into the bottom and sides. Trim any excess dough.
8. Fill the Tart: Pour the nectarine mixture into the crust, spreading it evenly.
9. Bake: Place the tart in the preheated oven and bake for 40-45 minutes, or until the crust is golden and the nectarines are tender.
10. Cool the Tart: Remove from the oven and allow it to cool in the pan for 15-20 minutes. Then, transfer to a wire rack to cool completely.
11. Dust with Powdered Sugar: Before serving, dust the top with powdered sugar for an elegant finish.

These steps will guide you in creating this incredible tart effortlessly.