In a bowl, mix spelt flour with cold butter, cold water, and salt. Shape the dough into a ball, then wrap it in cling film and put it in the fridge.

To prepare the filling, heat 3 tablespoons of olive oil in a pan over medium heat. Add mushrooms and fry for about 5 mins over medium heat. Add spinach leaves and fry for 1 min more. Set aside.

Preheat oven to 185 °C.

Flour the board. Once chilled, take the dough out of the fridge, knead it with bare hands and move it to the prepared board. Roll the dough into a circle (⌀ approx. 30 cm) with a rolling pin. The circle can be irregular, and the edges can be torn.

Cover a baking sheet with baking paper and place the rolled-out dough onto it. Layer the pan-fried filling, leek, and mozzarella in the middle of the rolled-out dough. Fold pastry edges towards the center of the galette.

Place the sheet in preheated oven and bake for 20 mins at 180 °C.

When baked, cut the galette into 8 pieces and serve.