Evening – Prepare the Levain

Combine all of the ingredients in a small mixing bowl. Beat with a spoon or whisk for about a minute, until the batter is mixed thoroughly and is fairly smooth. Cover the bowl with plastic wrap. Let it rest on the counter for about 12-14 hours, overnight. During this time, it should expand and become bubbly.

Make-Ahead Prep (while levain ferments):

• Caramelize the onions (takes about 45–60 minutes). Let cool completely, then refrigerate in a covered container overnight.

• Grate or cube the Gruyère cheese, and refrigerate in a sealed container until ready to use.

• This way, everything will be prepped when the levain is ready the next day.

• Optionally, prep the onions and cheese during the bulk ferment.

Next Day – Mix the Final Dough

In a large bowl, combine flour and 300 grams of water. Mix until no dry flour remains. Add in additional water, 1 tablespoon at a time, if needed

Cover and rest 30 minutes (autolyse).

Add levain (and yeast, if using). Mix thoroughly. Rest 20-30 minutes.

Add salt and incorporate with wet fingers. The dough should be soft but cohesive.

Bulk Fermentation (2.5–3 hrs at 76–78°F)

Perform 3-4 stretch-and-folds spaced 30–40 minutes apart.

Add the onions: After the 2nd fold, gently spread the caramelized onions across the dough, then fold to enclose and distribute them.

Add the cheese (choose one method):

• For grated Gruyère: Add during the final fold. Sprinkle the cheese evenly over the dough before folding so it gets layered in. This will create ribbons of melted cheese throughout the crumb.

• For cubed Gruyère: Add after bulk fermentation and before the 20-minute bench rest. Gently fold cubes into the dough just before pre-shaping. This will preserve distinct cheese pockets.

The dough should be airy and slightly domed at the end of bulk.

Shaping the Baguettes

Divide into 2 equal portions. Pre-shape each piece into a round, cover, and let them rest for 20 minutes.

Shape each into a 15-inch baguette, tapering the ends slightly. Place seam-side up in lined baguette proofing baskets. Cover and proof 45–60 minutes. Refer to this post for more details on shaping the baguettes.

Optional overnight rest in the refrigerator

Due to the increased hydration from caramelized onions and cheese, this can be a sticky dough. I found the shaped baguettes benefited from an overnight rest in the refrigerator before baking.

Cover, and let the loaves rise in the banneton baskets for one hour. Tightly cover with plastic wrap, and place in the refrigerator overnight.

Preheat the Oven

30-45 minutes before you plan to bake, prepare your oven for baking by placing one baking stone on the lower rack and another baking stone on the upper middle rack. If you’re only using one baking stone, place it on the middle rack.

Place a cast iron skillet, or other steam pan, on the bottom rack or floor of your oven. Preheat the oven to 450 degrees F.

Score & Bake

Turn baguettes seam-side down onto parchment.

Score 3–4 diagonal slashes with a lame at a 45° angle. Optionally, score the baguettes with one long score straight down the middle.

Using a baking sheet, load the baguettes (on the parchment) onto a baking stone, add steam (¼-cup boiling water) to the steam pan, and close the door.

Bake 12 minutes, rotate/move up, steam again, and bake 8–10 minutes longer (20–25 minutes total).

Cool on wire racks for at least 30 minutes.