This French Onion Mac and Cheese is made in one pot on the stovetop. The pasta cooks right in the sauce, soaking up flavor from caramelized onions and milk. It stays creamy for hours and even the next day. Just stir in a little milk to bring back its smooth, creamy texture.

Bowl of creamy French onion mac and cheese topped with caramelized onions and thyme, on a neutral napkin.

Why this recipe works

The secret to this French Onion Mac and Cheese is that everything cooks together in one pot, no boiling water or extra pans. This one-pot method lets the onions, milk, and pasta build flavor step by step, forming a rich base that thickens naturally as it cooks.

As it simmers, the pasta releases starch into the milk and water, helping the sauce thicken and the cheese melt smoothly.

The pasta absorbs some of the liquid while the rest turns into the creamy sauce. This balance keeps it rich but not heavy and still creamy even after it cools.

Ingredient notes and substitutions

Listed below are notes for the main ingredients. You’ll find all other details and exact amounts in the recipe card at the end of this post.

Pasta: I used elbow macaroni, but any short pasta like shells, penne, or fusilli works. Choose a similar size so it cooks evenly in the sauce.

Onions: Slice them medium-thick, not too thin. They shrink as they cook, so a little thickness gives the best sweetness and texture once caramelized.

Butter and Olive Oil: The mix adds flavor and helps prevent the onions from burning. You can use canola or sunflower cooking oil instead of olive oil if that’s what you have.

Thyme: Fresh or dried both work, about 1 teaspoon dried or a few sprigs fresh. Dried Italian seasoning also fits this recipe perfectly.

Sugar: Just 1 teaspoon helps the onions caramelize faster and balances the savory flavor. It won’t make the dish sweet.

Milk and Water: Any milk works — full-fat, 2%, or long-life (UHT). Full-fat gives the richest texture, while 2% or UHT still make a smooth, lighter sauce. The mix of milk and water keeps the sauce creamy but not heavy.
If using low-fat or long-life milk, add about 1 teaspoon olive oil, plus ¼ cup extra cheese at the end to keep the sauce smooth and creamy.

Cheese: Use what you have, Cheddar, mozzarella, or a mix.

Close-up of creamy French onion mac and cheese showing golden caramelized onions and thyme.

Step by step photos: French onion Mac and Cheese

These visual instructions help you see the process. You can also find the full printable recipe with ingredient amounts and instructions at the end of the post.

Step 1 and 2 showing sliced onions cooking in butter, then flour added to form the sauce base.

In a deep pot, melt butter and olive oil. Add sliced onions, sugar, and thyme. Cook for about 20 minutes, stirring often, until golden and soft. This is where all the flavor begins.
Scoop out 2 tablespoon (30 g) to save for garnish, then sprinkle in the flour and stir for 1 minute to coat the onions. This creates the base that thickens the sauce.

Make-Ahead Caramelized Onions

Caramelizing the onions takes about 20–30 minutes on low heat, with gentle, occasional stirring for that perfect golden color and rich flavor. You can cook the onions a day ahead to save time later.

Then cool and store them in an airtight container in the fridge.

When ready to make your mac and cheese, melt 1 teaspoon of butter in the pot, add the onions just to warm through, then continue with the recipe.

Step 3 and 4 showing milk and water being added to the pot with caramelized onions.

Gradually pour in the milk, stirring for 1 minute to mix with the onions and flour.
Add the water and stir for another minute.

Step 5 and 6 showing dry macaroni added to the creamy liquid and cooked until tender.

Add the uncooked pasta and salt.
Give it a gentle stir in the first minute, then again every 3–4 minutes as it cooks. Move it lightly so it doesn’t stick to the bottom, no need to stir constantly. Gentle movement keeps the sauce smooth and creamy without thickening too fast. Cook on medium heat for about 10–12 minutes, until the pasta is tender and the sauce thickens slightly and looks light and glossy.

Step 7 and 8 showing cheese stirred into the cooked macaroni and the sauce turning rich and creamy.

Take the pot off the heat and add in the shredded cheese.
Stir gently until the cheese melts and the sauce turns smooth and creamy. Taste and add a little more salt only if needed, some cheeses are already quite salty. Let it rest a few minutes before serving, the sauce will stay silky and creamy as it cools. Top with the reserved caramelized onions when serving.

Recipe tips

Adding the liquid and pasta: Pour in the milk and water, and stir gently for about 2 minutes to mix and warm it through. You don’t need to wait for it to bubble, just add the uncooked pasta and salt next. Keep the heat medium and steady, it will bubble gently and turn creamy as it cooks.

Salt: Add the salt with the liquid and pasta so it seasons the sauce as it cooks. Taste again after adding the cheese and adjust only if needed, some cheeses are saltier than others.

Different pasta shapes cook differently: Smaller shapes (like elbows or shells) cook a little faster than thicker ones (like penne). Start checking a minute or two before the time recommended on the package. The pasta should be tender but still hold its shape.

Storage and reheating

Store any leftovers in an airtight container in the fridge for up to 3 days. The sauce stays creamy even after cooling.

Just stir in about 1–2 tablespoons of milk per serving) when reheating to bring back the silky texture.

Reheat gently on the stove over low heat, or in the microwave on medium, stirring halfway through. Avoid high heat, it can make the sauce thicken too much.

Watch how to make it

Recipe