Roll the sole fillets, starting from the widest part, and hold them rolled with a toothpick.
Bring the fish stock to a boil and cook the rolled sole fillets and shrimp for 10 minutes.
Drain the sole fillets and shrimp, and reserve 1 and 1/2 cups (375 ml) of fish stock.

Melt the butter in a saucepan. Cook the shallot, celery, and mushrooms until they are tender.
Sprinkle with flour, mix quickly with a wooden spoon to make a roux.
Add the fish stock, and mix until the mixture thickens.
Add the lemon zest and juice, and parsley.
Season with salt and pepper to taste.

In a bowl, beat the egg yolks with the cream using a fork.
Add the mixture to the saucepan, stir to combine, but do not let it boil.
Add the sole fillets and shrimp to the sauce to heat them through.
Serve immediately with basmati rice and spinach.