4Trim the edges of the pastry so it resembles a rough oval shape and place onto the prepared baking tray. Using half the feta, arrange a layer of the cheese on the pastry leaving a 4cm border, followed by the caramelised onion. Now arrange a layer of the sweet potato slices over the top, working in a circle with slices overlapping, until all the slices are used.
5Now fold the border of the pastry inwards, brush with egg yolk, and top the sweet potato with remaining feta.
6Bake in the oven for 15-20min or until golden brown. Top the galette with fresh herbs like thyme and sage, drizzle with olive oil and season with salt and pepper.