French Onion Tart

✅Ingredients

1 sheet puff pastry, thawed
2 large Vidalia onions, thinly sliced
2 tablespoons unsalted butter
1/2 cup beef stock
1 teaspoon fresh thyme leaves (or 1/2 teaspoon dried thyme)
1/4 cup grated Gruyère or Swiss cheese
Salt and pepper to taste
1 egg, beaten (for egg wash)
✅Instructions
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