Rustic Onion Tart Recipe

Ingredients

• 1 1/4 cup (160 g) all purpose flour
• 1 teaspoon salt
• 5 ounces of butter (1 1/4 sticks, 10 Tbsp, 137g), cubed
• 1/4 cup sour cream
• 3 medium sized red and/or yellow onions (enough for 5 to 8 cups, sliced)
• 2 tablespoons extra virgin olive oil
• 1 tablespoon butter
• Kosher salt
• 1 teaspoon balsamic vinegar
• 3/4 cup (not packed) roughly grated Gruyère Swiss cheese
• 1/2 teaspoon fresh thyme, chopped, or 1/4 teaspoon dried thyme