Sift 200 g plain flour into a large mixing bowl. Add 100 g salted butter (cubed), and use your hands to rub it into the flour. Continue, until the mixture resembles breadcrumbs. Next, add 3 tablespoon milk or water (cold), and gently knead until the mixture holds together. Form into a ball, cover with reusable wrap, and chill for a minimum of 30 minutes.
Make the Galette Filling
Preheat the oven to 180℃ (356℉).
Add 100 g feta cheese, 20 g mixed herbs, black pepper (to taste), sea salt (to taste), and 1 lemon, zested (just zest, not juice) to a blender. Blend to a paste.
Use a knife or mandoline to slice 160 g courgette into small rounds.
Make the Garlic Butter
Heat 20 g salted butter in a small saucepan over low heat. Add 4 cloves garlic (crushed), and cook low and slow, until the butter smells gloriously aromatic and the garlic has slightly browned. Turn of the stove and set aside.
Assemble the Courgette Galette
Gently flour a clean, flat surface. Use a rolling pin to roll the chilled pastry into a circle roughly 30cm in diameter. Leave the edges rough for a rustic look or trim to make it look more professional. Slide onto a lined baking tray.
Spread the feta/herb/lemon mixture over the base of the galette, leaving the edges of the pastry plain. Next, arrange the courgette slices on top, and pour over the garlic butter.
Fold the edges of the pastry over the courgette, and brush with 1 medium egg yolk (whisked). Sprinkle sea salt flakes and ½ teaspoon nigella seeds over the edges.
Bake the Courgette Galette
Bake for 20-30 minutes, until the galette pastry has turned golden. Remove from the oven and garnish with rocket leaves (arugula) and any excess garlic butter.
Notes
For an even prettier galette, you can use a mix of green and yellow summer squash (courgette or zucchini).