Caramelized Onion Pasta
Sweet, jammy caramelized onions are tossed with pasta in a simple, savory cream sauce with Parmesan and thyme.
Ingredients
- 1 lb dried pasta such as fettuccine or rigatoni, 454g
- 2 tbsp olive oil 30ml
- 4 tbsp unsalted butter divided, 57g
- 2 large yellow onions thinly sliced, about 2 lbs / 900g
- 1 tsp salt plus more for pasta water
- 4 cloves garlic minced
- 1/2 tsp red pepper flakes optional
- 1 1/3 cups heavy cream 320ml
- 1 cup finely grated Parmesan cheese 100g
- 2 tbsp fresh thyme leaves
- 2 tbsp fresh lemon juice
- Freshly ground black pepper to taste
- Lemon zest for serving, optional
Instructions
- In a large, heavy-bottomed pot or Dutch oven, heat the olive oil and 2 tablespoons of butter over medium heat. Add the sliced onions and cook, stirring occasionally, for 10 minutes until they have softened.
- Stir in the salt. Reduce the heat to low and continue to cook the onions for 40-50 minutes, stirring every 5-10 minutes to prevent sticking. The onions should be a deep golden brown and very soft. If they start to dry out, add a tablespoon of water.
- When the onions are nearly done, bring a large pot of salted water to a boil. Cook the pasta according to package directions until al dente. Before draining, reserve about 2 cups of the pasta water.
- While the pasta cooks, return the onion pan to medium heat (or use a separate large skillet). Melt the remaining 2 tablespoons of butter. Add the minced garlic and red pepper flakes, if using. Cook for 1 minute until fragrant, but do not let the garlic brown.
- Pour in the heavy cream and bring to a gentle simmer. Reduce the heat to low. Add the Parmesan cheese in small batches, stirring until each addition is melted and the sauce is smooth. Stir in the fresh thyme.
- Drain the pasta and add it directly to the skillet with the cream sauce. Add the caramelized onions, lemon juice, and 1/2 cup of the reserved pasta water.
- Toss everything together over low heat for 1-2 minutes, allowing the sauce to coat the pasta and thicken slightly. Add more pasta water, a tablespoon at a time, to reach your desired sauce consistency. Season with black pepper.
- Serve immediately, garnished with extra Parmesan cheese and lemon zest if you like.
Notes
Patience is key for caramelizing onions. Low heat and time are required to develop their deep, sweet flavor. Do not rush this step.
Always reserve more pasta water than you think you need. The starchy water is essential for creating a silky sauce that clings to the pasta.
For the smoothest sauce, use a block of Parmesan cheese and grate it yourself on the finest setting of a box grater or with a microplane.
The sauce will thicken as it cools. Keep it a little looser in the pan than you want it on the plate.