Step 1

Soak the chiles in hot water to soften. Meanwhile, put the yolk, lemon juice, mustard, and garlic in a blender or food processor and turn the machine on. While it’s running, add the oil in a steady stream. When an emulsion begins to form, you can add the oil a little faster.

Step 2

Drain the chiles and remove their seeds; add them, along with the red pepper, and continue to blend until the mixture is smooth. Add salt and cayenne if necessary (the rouille should be quite hot). Taste and add more salt or lemon juice if you like. Best served immediately, but keep it for a few hours if you must.