Make the pie dough following this recipe. Alternatively, you can buy premade pie dough to save time for this recipe.
If making the pie dough, let it chill in the fridge for at least 2 hours, wrapped tightly in plastic wrap.
Make the caramelized onion filling. Heat olive oil in a large stainless steel skillet over low-medium heat. Add the onions and toss in the oil. Cook the onions for 30-45 minutes, stirring occasionally. When you notice brown, caramelized bits sticking to the pan, add a tablespoon of water to loosen them and mix them into the onions. Once the onions are sweet and light brown, they’re ready.
Add the kale to the onions, stirring to combine everything and evenly coat the kale in olive oil. Let the kale cook for 2-3 minutes until wilted.
Preheat the oven to 375 degrees.
Roll out the pie dough into a circle as best you can, about half a centimeter thick. Use a floured surface, and flour the top of the pie dough to prevent sticking.
Transfer the pie dough to a parchment paper lined baking sheet. An easy way to do this is to roll the pie dough onto your rolling pin, then gently roll it out on the baking sheet.
Spread the goat cheese in an even layer on the pie dough, leaving 1-2 inches border.
Top the goat cheese with the onions and kale mix.
Arrange the apple slices in an even layer on top of the onions and kale.
Fold up the edges of the pie dough to “tuck in” the ingredients. Make sure to overlap your folds so everything is wrapped up.
Sprinkle with rosemary, salt and pepper.
Bake for 35–45 minutes, until the pie dough is crispy and hard to the touch.
For best results slicing, let the galette cool to room temperature before cutting into it.
Keeps in the fridge for up to 2 days in the fridge, in an airtight container or wrapped in plastic wrap.