Preheat the oven to 400°F. Line a cookie sheet with parchment or wax paper.
In a stand mixer, combine the Bob's Red Mill Gluten Free 1-to-1 Baking Flour, salt and sugar. Mix thoroughly. Then add the softened butter to the mixer and mix until a large clump of dough is formed (mixing approximately 2 minutes). Add the cold milk to the stand mixer and mix until it is fully integrated with the dough.
Remove the dough from the mixer and form into a round disk shape. Place on the parchment paper lined cookie sheet and cover tightly with plastic wrap. Place in the refrigerator to chill for approximately 30 minutes.
To make the filling, combine the blueberries, blackberries and brown sugar in a bowl. Slice the nectarine thinly and dice the candied kiwi, set aside.
Once the dough has been chilled, remove it from the refrigerator. Using your hands or a rolling pin, flatten out the dough into a rough rectangular shape. The dough should be approximately 1 centimeter thick throughout. Spread the berries-sugar concoction in the center of the dough and then fold over the dough edges. Brush the outside of the galette with egg yolk and then place in the oven. Bake for approximately 20 minutes.
After 20 minutes, remove the galette and place the nectarine slices on top of the tart. Place back in the oven for another 15 to 20 minutes.
Remove from the oven and let cool. Garnish with the candied kiwi and enjoy!