Onion Tart

1. Caramelize the Onions

Heat the olive oil or butter in a low-sided heavy-bottomed pan over medium heat. Add the sliced onions and thyme sprigs to the pan, cooking them slowly for 20 to 30 minutes until caramelized. Season with salt and cook for a few more minutes.

2. Cool the Onion Mixture

Transfer the caramelized onions to a bowl to cool. Strain off excess liquid if necessary and remove the thyme sprigs.

3. Prepare the Dough

Roll out the tart and pie dough into a 14-inch circle on a lightly floured surface. Brush off any excess flour and transfer the dough to a baking sheet lined with parchment paper. Chill in the refrigerator for 10 minutes.

4. Assemble the Galette

Spread the cooled onions over the dough, leaving a 1.5-inch border around the edges. Fold the dough border up over the onions to create a rustic edge.

5. Prepare Egg Wash

In a small bowl, mix the egg with the milk or water to make an egg wash. Brush this over the folded dough rim.

6. Bake the Galette

Preheat the oven to 375°F. Place the galette on the bottom rack and bake for 45 to 50 minutes, or until the crust is golden brown.

7. Cool and Serve

Remove the galette from the oven and let it cool on a rack. Serve warm or at room temperature.