Pulse the flours, polenta, xanthan gum, baking powder and salt in a food processor to combine. Add the butter and pulse until the mixture resembles fine breadcrumbs.

Transfer to a bowl, add the potato and sesame seeds and mix well with your hands until dough feels smooth and elastic.

Knead the pastry for 2–3 minutes until smooth. Shape into a ball, cover with plastic wrap and refrigerate for 30 minutes.

Preheat the oven to 180°C.

Lightly grease a 30 x 21cm loose-based flan tin.

Roll out the pastry to form a 32 x 23cm rectangle on a lightly floured surface. Press into the prepared tin, covering the sides and edges, and line the pastry shell with baking paper and pastry weights or uncooked rice. Blind bake for 15 minutes. Remove the baking paper and pastry weights and return the pastry case to the oven for a further 5–7 minutes, or until golden. Set aside to cool slightly.

Increase the oven to 200°C.

Melt the butter and oil in a large frying pan over medium heat.

Add the onion and garlic and cook, stirring, for 15 minutes, or until soft and golden. Season well with salt and pepper.

Whisk the eggs, egg yolks and cream in a large bowl. Stir in the onion mixture, tomato and thyme, then pour into the pastry case. Crumble the goat’s cheese over the top and bake for 25 minutes, or until golden.

Garnish with the extra thyme, season with some more pepper and serve.