Muscle Momma Sourdough

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French onion soup… but baked into a sourdough loaf!

I’ve always loved the sweet & savory balance of caramelized onions, and let’s be real, putting them in a sourdough loaf just made sense.
An onion lover’s dream, this loaf is like French onion soup in bread form: soft on the inside, crisp on the outside, and loaded with cheese and onions in every bite.

Let’s get into it!

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Step 1: Mix Your Dough

In a large mixing bowl, stir together 100g active sourdough starter, 375g filtered water, 1 packet of onion soup mix (or about 115g homemade mix) The onion soup mix is optional but adds great flavor!

Now add the dry ingredients: 450g unbleached bread flour and 50g whole wheat flour. Use a dough whisk to mix everything until no dry bits remain. The dough will look shaggy and rough, not like a smooth ball. Cover and let it rest for 1 hour.

*You may notice there is no salt in this recipe, that’s because the onion soup packet has plenty of salt for the amount of dough. If you make your own mix or skip the onion soup packet, be sure to add 10g additional salt to the dough.

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Step 2: Caramelize Your Onions

While your dough is resting, start caramelizing the onions:

• Thinly slice (julienne) 2 yellow onions
• Heat a cast iron skillet over medium-high heat and add a splash of oil.
• Add the onions and cook for about 10 minutes, stirring constantly to prevent burning.
• Once softened and starting to brown, reduce the heat to low.
• Continue cooking low and slow, stirring occasionally to prevent burning.
• If the onions begin to dry out, add 2–3 tablespoons of water and cover the pan briefly to rehydrate.
• Add a pinch of salt to enhance flavor.
• Cook until the onions are soft, golden, and jammy (about 30–40 minutes total).

Tip: Don’t rush this step—low and slow brings out the best flavor.

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Step 3: Strengthen the Dough

After the rest, it’s time for stretch and folds. You’ll do 3–4 sets of folds every 30 minutes. We’ll add inclusions during the second fold.

Here’s the plan:

• 1st Fold: Just a basic stretch and fold to strengthen the dough
• 2nd Fold: Add caramelized onions + cheeses (details below)
• 3rd Fold: Use coil folds for strength and to keep inclusions inside
• 4th Fold (optional): Add only if needed

How to Add the Inclusions During the 2nd Fold:

• Uncover your dough
• Evenly scatter some of the cooled onions, shredded Gruyère, and shredded Parmesan over the dough
• Stretch the dough up and fold over on inclusions
• Sprinkle more of the inclusions over the top layer and continue folding on all four sides
• Gently tuck the dough under itself and cover
• Reserve a small handful of cheese and onions for topping later (optional)

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Step 4: Bulk Fermentation

Let the dough rise until it’s about doubled in size, bubbly, jiggly, and slightly domed.

Bulk Fermentation time greatly depends on your dough temperature. I like to use this as a guideline. The fermentation time starts from the moment you mix your dough in Step 1.

Dough Temperature vs. Bulk Fermentation Time

80°F (27°C) → ~5-6 hours

75°F (24°C) → ~7-8 hours

70°F (21°C) → ~12 hours

65°F (18°C) → ~16 hours

Use this chart as a guideline—not a rule. I mostly rely on visual cues to know when my dough is ready.

For reference this dough was 78°F, and took around 7 hours from the time of mixing the dough.

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Step 5: Shape & Cold Proof

Shape Your Dough:

• Turn the dough out onto a clean surface
• Preshape into a round boule using a bench scraper
• Let rest uncovered for 30 minutes
• Final shape into a boule.

If you need a shaping tutorial, I have one here.

Cold Proof:

• Place seam-side up in a floured banneton
• Cover and refrigerate for 12–24 hours

Same-day option: Proof in a warm spot for a few hours before baking.

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Step 6: Bake

• Preheat a Dutch oven at 450°F for at least 30 minutes
• Flip your dough onto parchment paper, score it, and transfer to the hot Dutch oven

• Bake covered at 450°F for 35 minutes
• Uncover, add reserved onions and cheese to the top, and bake 10–15 minutes more until golden

Final Temp: 205°F internal
Cool: Let cool on a wire rack at least 1 hour before slicing

Frequently Asked Questions

I don’t want to use store-bought onion soup mix—can I skip it?

Totally! The soup mix adds extra flavor and salt, but it’s optional. If you’d rather make your own, there are a ton of great DIY onion soup mix recipes just a quick Google away. Just be sure to add salt if your homemade version doesn’t include it.

How should I serve this bread?

Honestly? It’s incredible just plain and warm from the oven. But imagine this as the base for a grilled cheese! Add melty fontina or more Gruyère and dip it in soup? Unreal.

Can I freeze this bread?

You can! Let the loaf cool completely, keep whole OR pre slice, then place it in a freezer-safe bag. It’ll keep well for about 1-2 months.

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