Leek and Onion Tart with Gruyere

Preheat oven to 375°F (190°C).

In a large skillet over medium heat, melt butter with olive oil. Add leeks and onions, season with salt and pepper. Cook, stirring occasionally, until softened and caramelized, about 25-30 minutes. Reduce heat if needed to prevent burning.

If using, add white wine and cook for another 2-3 minutes, scraping up any browned bits from the bottom of the pan. Stir in thyme.

While the leeks and onions are cooking, unroll pie crust and fit it into a 9-inch tart pan, trimming any excess dough. Prick the bottom of the crust with a fork.

In a medium bowl, whisk together eggs and heavy cream. Season with salt and pepper.

Spread the caramelized leek and onion mixture evenly over the pie crust.

Sprinkle the shredded Gruyere cheese over the leek and onion mixture.

Pour the egg and cream mixture evenly over the leeks, onions, and cheese.

Bake for 30-40 minutes, or until the crust is golden brown and the filling is set. A knife inserted near the center should come out clean.

Let the tart cool slightly before slicing and serving.