In the bowl of a stand mixer fitted with the paddle attachment, add the butter and granulated sugar and beat on medium speed for 1-2 minutes until mixed together evenly.
Add the egg yolks one at a time, then the flour and salt until the dough just comes together. Turn the mixer off and use a spatula to scrape the bottoms and sides to make sure homogenous.
Butter the sides and bottom of a 9-inch springform pan. Pour the dough into the pan and spread it evenly along the bottom of the pan and up the sides, it should reach about 2 inches up the sides. Use the bottom of a cup or the palm of your hand to get the dough as even as possible.
Freeze the dough in the pan for 30 minutes
To make the Crumble Topping
Using a food processor, pulse the almonds, flour, brown sugar, cinnamon, and salt together until the almonds are in very small pieces.
Add the cold butter pieces and pulse another 10-20 times, until the mixture just starts to form small clumps.
Chill the crumble until ready to use
Bake the Tart Shell
Preheat the oven to 375° F
Remove the tart shell from the freezer and line with aluminum foil and cover with pie weights (I always use dried beans!).
Bake for 20 minutes, then remove the foil/weights and bake for 5-10 minutes more until brown. Remove from the oven and set aside.
Turn the oven down to 350° F
To Assemble and Bake the Tart
Combine the nectarines with the sugar, cornstarch, vanilla extract, almond extract, and salt in a medium bowl. Stir gently to coat.
Transfer the filling to the baked tart shell and gently even it out with a spatula to fill any holes.
Sprinkle the crumble topping evenly over the topping.
Bake the tart for 50-60 minutes, until the crumble is nicely browned. The tart crust may look dark at this point but shouldn’t taste burnt.
Let cool in the pan on a wire rack for 5-10 minutes. Run a knife around the edge of the pan to loosen the crust and remove the sides of the springform pan.
Serve warm or at room temperature with a scoop of ice cream or whipped cream.