Pour in the reserved sauce mixture, stir-fry briefly, then serve.

Pour the remaining stock into the pan containing the sauce mixture.

Spoon on half the mozzarella and white sauce mixture.

Toss in the sorrel and stir into the sauce mixture.

Add the remaining sauce mixture to the liquid in the saucepan, and quickly bring to a simmer.

Carefully fold the egg white into the sauce mixture.

Increase the heat to high and add the sauce mixture.

Baste frequently with the sauce mixture to maintain the moisture.

Add the combined sauce mixture and stir until thickened.

Add the pasta to the sauce mixture and toss.