To make the galette dough: Place flour and salt in the bowl of a food processor. Pulse for a few times to mix. Add in the cold butter cubes. Pulse 8-10 times until butter resembles small clumps.
Turn the machine on and add in 4 tablespoons of ice-cold water in one tablespoon increments.
At this point, it should start to come together and form into a ball. If not add in the rest of the water until it does.
Transfer onto a lightly floured surface, form it into a 4-inch disk, and wrap with plastic. Place in the fridge for at least 1 hour or overnight.*
Take it out of the fridge 10 minutes before you are ready to roll it out.
To make the filling: Place peaches, plums, blueberries in a bowl. Sprinkle it with coconut sugar. Set it aside to macerate.
Pre-heat the oven to 375 F degrees (190 C.) Prepare a sheet of parchment paper that will fit into the baking sheet.
To assemble: Lightly flour your working surface. Roll the dough into a large 12-inch circle. Transfer onto the parchment paper and then onto the baking sheet.
If you are using, sprinkle it evenly with almond meal leaving a 2-inch border on the sides.
Spread the fruit on top slightly mounting in the middle, again leaving a 2-inch border around the edges.
Roll the sides of the dough overlapping as you go around and pleating the dough.
Whisk egg with a tablespoon of water to make egg wash.
Brush the outer crust with egg wash and sprinkle with sliced almonds lightly pressing to make sure they stick.
Bake 50-55 minutes or the crust turns golden brown. Transfer the galette onto a wire rack to cool.
If preferred, dilute honey with a tablespoon of water and lightly brush the top of the fruit.
Serve while it is still warm.