Slice butter into ½-inch cubes and place back into the freezer to chill until you're ready to add it to the dough for the crust.
Add the rest of the ingredients for the dough to a mixing bowl: flours, sugar, sea salt, and butter. Mix the butter into the dough as much as you can. Make a well in the center and add the apple cider vinegar and ice cold water, 1 tbsp at a time. Add water until it comes together. If you make it too wet, add some more flour until it comes together into a neat ball of dough. Cover the bowl and refrigerate for at least an hour or even overnight. Preheat the oven to 400 F and let the crust dough sit at room temperature for about 15 minutes.
For the jam, microwave 3 apricots for about 30 seconds until soft. Mash with a fork. Microwave for another 15-30 seconds. Then mix in the maple syrup, lemon juice, and chia seeds.
For the filling, thinly slice the apricots and toss with maple syrup, lemon juice, and cornstarch.
To assemble, split dough into three parts (see note 1 for alternative). Roll each one out until 1/4-inch thick. Split jam equally between the three galettes. Split filling equally between the three galettes.
Bake for 20-30 minutes (this depends on size of your galettes), or until the crust is nicely browned and crisp. It should take closer to 30 minutes.
Serve with ice cream!
