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Makes

6 servings

Ingredients

  • 1 ½ tablespoons olive oil
  • 2 tablespoons butter
  • 1 large yellow onion thinly sliced
  • Salt and freshly ground black pepper to taste
  • 1 pound fresh spinach washed and stems removed (or use 10 ounces frozen spinach, thawed and drained)
  • 2 cloves garlic minced
  • 4 large eggs
  • ¾ cup half-and-half
  • 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme
  • Pinch of nutmeg
  • 1 cup grated Gruyère cheese
  • ¼ cup freshly grated Parmesan cheese
  • 1 prepared tart or pie shell 9-inch, homemade or store-bought

Instructions

  • Preheat the oven to 375°F.
  • In a large skillet, heat the olive oil and butter over medium-low heat. Add the onions, garlic, and a pinch of salt, cooking slowly until the onions are deeply golden and caramelized, about 20–25 minutes. Stir occasionally to prevent burning. Once caramelized, set aside.
  • In the same skillet, add the spinach and cook until wilted, about 4–5 minutes. If using frozen spinach, skip the cooking step. Once wilted, transfer spinach to a colander and press firmly to expel excess water, making sure to get the spinach as dry as possible. Roughly chop and set aside.
  • In a large bowl, whisk together the eggs, half-and-half, thyme, nutmeg, salt, and pepper. Stir in the Gruyère, Parmesan, caramelized onions, and chopped spinach, mixing until well combined.
  • Pour the filling into the shell, spreading it evenly. Bake for 35–40 minutes, until the filling is set and lightly golden on top. Remove from the oven and allow to cool slightly before slicing.
  • This tart can be served warm or at room temperature. Pair with a crisp side salad or roasted seasonal vegetables for a full meal.
  • Chef’s note: To bring a Maine touch, try adding a sprinkle of smoked Maine sea salt on top after baking, or incorporate a handful of locally foraged mushrooms with the onions for added depth. This tart makes an elegant, hearty centerpiece for any table, blending New England produce with French-inspired flair.