Mix together flour, sugar and salt in a large bowl. Add the sliced or diced butter to the dry ingredients, and using your fingers, work the butter until the dough is crumbly but there are still some small visible pieces of butter.
Separate the thyme leaves from the twigs and add them to the dough. Drizzle the dough with ice water, 1 tbsp at a time, and mix just enough so that the dough comes together. Do not knead the dough.
Form the dough into a ball and place it on a piece of plastic wrap. Flatten into a disc, wrap in the plastic wrap and place in the fridge for at least one hour but preferably overnight.
Filling, Assembly & Baking
Preheat the oven to 200°C (390°F).
Cut the rhubarb stalks and the peaches and place them in a bowl. Add the lemon juice, 30 g of sugar and mix.
Roll out the dough into a large circle 3-5 mm thick, on a lightly floured surface. Make sure to roll and turn the dough so it doesn’t stick to the surface.
Using the rolling pin, transfer the dough to a baking sheet covered with baking paper.
In a bowl, mix the ricotta cheese, 30 g of sugar, the vanilla extract and the lemon zest.
Place the ricotta filling on the dough, leaving a border around the edges, that you will eventually fold.
Add the fruits on the ricotta filling, fold the dough over the fruits and press gently to seal. Keep 1-2 tbsp of fruit juice.
Brush the edges of the galette with some of the juice from the fruits and sprinkle with some sugar.
Bake in the middle rack until golden brown, about 35-40 minutes. Let cool, then serve with additional thyme twigs, sprinkled with honey.