For the pastry, place the flour, sugar, and salt in the bowl of a food processor and pulse a few times to combine. Add the butter and pulse 12 to 15 times, or until the butter is the size of peas. Drizzle the ice water all around and pulse until the dough is almost a solid mass. Form the dough into a disk and wrap in plastic. Refrigerate for 20 minutes.

For the topping: Combine the flour, ¼ cup sugar, and salt, (and spices if you are using any) in the bowl of a food processor. Add the butter and pulse until the mixture is crumbly. Pour into a bowl and rub it with your fingers until it starts holding together. Refrigerate until needed.

Turn the dough onto a well-floured board and roll into an 11-inch circle. Transfer it to a baking sheet fitted with a Silpat liner if you have one or parchment paper for easier clean up.

Preheat the oven to 450 degrees F.

Place the nectarines and blueberries in center of dough leaving a 1 1/2-inch border and sprinkle with 1 tablespoon sugar.

Sprinkle the streusel topping evenly on the nectarines. Gently fold the border over the nectarines to enclose the dough, pleating it to make a circle. Brush crust with half and half and sprinkle with sugar.

Bake the galette for 20 to 25 minutes, until the crust is golden and the nectarines are tender. Allow to cool. Serve warm or at room temperature.