Mornay Sauce Recipe: a Creamy French Classic

In a heavy-bottomed saucepan over medium-low heat, melt the unsalted butter. Whisk in the flour to create a roux, cooking for 2-3 minutes until it smells like toasted shortbread but remains blonde.

Gradually whisk in the 2% milk and vegetable stock, ensuring no lumps form. Add the onion half and the bay leaf to the liquid.

Simmer the sauce gently for about 10 minutes, whisking frequently, until the mixture thickens enough to coat the back of a spoon.

Remove the onion and bay leaf. In a small bowl, whisk together the egg yolk and light cream to create a liaison.

Temper the yolk mixture by slowly drizzling in a few tablespoons of the hot sauce while whisking. Pour the tempered mixture back into the saucepan, whisking constantly.

Add the grated Gruyère and Parmigiano-Reggiano. Stir until the cheese is completely melted and the sauce is glossy.

Season with nutmeg, white pepper, and sea salt. For a perfectly smooth texture, pass the sauce through a fine-mesh sieve before serving.