Ingredients :

• The bread — sourdough as a priority — Sourdough is my default choice. Robust enough to hold up without getting soft, and its slight acidity against the melted cheese creates a real balance. Avoid standard sandwich bread: too thin, it browns in 40 seconds before the cheese even starts to melt. Aim for a thickness of about 1.5 cm — the format that gives the cheese time to catch up with the bread.
• The cheese — the cheddar + gruyère duo — On its own, cheddar is too compact to stretch properly. On its own, gruyère can become a bit bland when hot. Together, you get the sharp taste of the first and the silky texture of the second. Grate them yourself — pre-shredded supermarket cheese contains an anti-caking agent that prevents even melting. This step makes a real difference, not an imaginary one.
• The butter — soft, not melted — The distinction is vital here. Melted, the butter goes directly into the pan and burns too quickly, leaving irregular dark spots. Soft, you spread it directly on the bread — it creates a uniform layer that browns homogeneously, like light caramel over the entire surface. Unsalted butter is preferred to keep control over the salt.
• Sea salt flakes — optional in theory only — Three small pinches on top of the buttered bread before cooking. The salt enhances the cheese in a way that cannot be reproduced otherwise. It’s the kind of detail that makes guests say they don’t know what’s different, but it’s better. Do not replace with fine salt — sea salt crystals behave differently during cooking.