Start by making the pastry. Add 300 grams (2 cups) flour, 1 teaspoon coconut sugar, and 1/2 a teaspoon salt to a large mixing bowl and whisk to combine.
300 grams spelt flour, 1 teaspoon coconut sugar, 1/2 teaspoon sea salt
Add 60 grams (1/4 cup) coconut oil and use your hands to mix until a sandy texture forms.
60 grams solid coconut oil
Add four tablespoons of ice water to the mixture and mix to combine. Add the remaining water a tablespoon at a time, mixing quickly between each addition, until the dough holds when pressed. You may not need all of the water.
4-6 tablespoons ice water
Cover the bowl with a plate and set aside. If your kitchen is very warm, place the dough into the refrigerator while you prepare the filling.
To make the filling, scrub 600 grams (21 oz.) potatoes. Slice them as thinly as possible, using a mandoline or the slicing attachment on your food processor.
600 grams potatoes
Place the sliced potatoes into a large bowl and add 1 tablespoon olive oil, 1 teaspoon thyme, 1 teaspoon salt, and 1/2 teaspoon pepper.
Mix until the potatoes are fully coated and set aside.
Preheat the oven to 190°C (375°F).
To assemble, roll out the pastry to a round about 30cm (12 in.) in diameter.
Carefully lift the pastry and place it onto a sheet of parchment paper. Transfer, with the paper, to a large round tart tin, or onto a large baking sheet.
Add the caramelised onions in an even layer over the pastry, leaving a rim of pastry that can be folded over.
100 grams caramelised onions
Fill with the potatoes, reserving enough to make a pattern on top. Arrange the reserved potatoes in a spiral or other pattern.
Fold the pastry over, gently pressing to seal any places where it folds over itself. Brush with olive oil (optional).
Bake the galette for 35-40 minutes, or until the pastry and top layer of potatoes are golden brown. Cool for about ten minutes before slicing and serving.
Leftovers keep well for a day or two at room temperature. I haven't tried freezing this.