Line a rimmed baking pan or sheet with parchment paper. (Because of the liquidy nature of the filling, we baked this galette on parchment inside a rimmed baking dish, which, it just so happens, was a tart pan. You could alternatively place the galette on a rimmed baking sheet; or, you could take a risk and put it right on an unrimmed baking sheet—if you do, however, know some of the juices may leak while the galette bakes.)
In a medium bowl, combine flour and salt.
Cut in the cubed butter with a pastry cutter or forks or, potentially, inside a food processor.
Add water and yogurt; stir until it comes together; use your hands to form the dough into a ball.
Roll out on a floured surface to be larger than you’d like your galette to be. I was baking in a 10-inch-round tart pan, so I made my dough circle slightly larger than that. Place on baking sheet or pan. While you make the filling, stick this dough in the fridge to keep it cold.
Preheat oven to 350F.
To make the filling, combine grapes, coconut sugar, arrowroot powder, thyme and lime juice; stir to coat.
Pull out the galette dough. Pile the filling in the center and fold the edges on top of the grapes, pleating it as you do. The idea is just to get the edges folded up and over the filling to keep them securely inside while they bake.
Brush the dough with yogurt all over. This will give the galette a beautiful golden crust.
Place galette in the oven for about an hour, give or take ten minutes. Rotate once halfway through, and start checking for doneness at around 45 minutes of bake time.