1. Preheat the oven to 375°F (190°C). Butter a 9 × 13in (23 × 33cm) baking sheet and line with parchment paper.

2. Melt the butter in a large saucepan over medium-low heat. Whisk in the flour and let bubble for 1 minute. Gradually whisk in the milk and cook, whisking often, until the sauce comes to a boil. Remove from the heat again and stir in half of the Parmesan. Add the mustard and season with salt and pepper. Allow to cool slightly, then beat in the egg yolks.

3. Beat the egg whites in a bowl until they form soft peaks. Stir one-fourth of the whites into the cheese mixture to lighten it, then fold in the remaining whites. Spread evenly into the prepared pan.

4. Bake for about 20 minutes, or until golden and the top springs back when pressed. Turn out on to a large piece of wax paper dusted with the remaining Parmesan.

5. Peel away the parchment paper and trim off the crispy edges from the roulade. Spread the surface with the ricotta, leaving a 1in (2.5cm) border at the short sides. Cover the ricotta with the arugula. Roll up the roulade lengthwise, using the paper as an aide. Cut into slices, and serve.

Variations:

Mix a pinch of nutmeg into the ricotta before spreading over the roulade. Replace the arugula with spinach and add 3 oz (85g) roughly chopped sun-dried tomatoes before rolling in step 5.