Method

1. Preheat the oven to 220C/425F/Gas 7.
2. Whisk the egg whites until soft peaks, add the flour and whisk to form stiff peaks.
3. In bowl, mix together mustard and egg yolks. Fold in the egg whites to combine.
4. Smooth out the mixture onto a baking tray lined with Teflon. Scatter the herbs over and then scatter with the cheese and spinach.
5. Bake in the oven for 8-10 minutes, or until golden and cooked through.
6. Remove from oven and once cool enough to handle, roll up to make a roulade.
7. Serve.