Preheat oven to 375 degrees F (190 degrees C).
In the bowl of a food processor combine Gluten-Free All-Purpose Flour (1 1/2 cup) Muscovado Sugar (1/4 cup) Baking Powder (1/2 teaspoon) and Salt (1 pinch) - pulse to combine
Add Unsalted Butter (1/2 cup) pulse to combine.
Add the whole Egg (1) and 1 egg yolk. Process until a soft dough forms.
Turn the dough out onto a work surface and knead just until it comes together.
Evenly press dough into the bottom and up the sides of a 10.5" fluted tart pan with removable bottom.
Spread Peach Jam (1/2 cup) on top of dough.
Lay White Peach (3) atop the jam filled crust in concentric circles.
Bake the tart for 20 minutes.
Remove from oven and brush peaches with remaining Peach Jam (2 tablespoon).
Return tart to the oven and bake for another 20 minutes.
Lightly dust tart with Powdered Confectioners Sugar (1 tablespoon) and leave to cool for at least 30 minutes before slicing and serving.