Champagne AND Salmon? Ooh, you are really spoiling them!
You can prep the sauce and salmon hours before you need to serve. Just warm the sauce up and off you go
Heat the oven to 200.
First make the roux in a pan using the butter and flour. Melt the butter first until it foams and add flour, keep stirring and cook for 3 minutes.
Add the fish stock gradually and whisk so the sauce is smooth.
Add the white wine and leave to simmer for 15 minutes
Slice the shallots and place in an oven proof dish.
Lay the salmon on top of the shallots, season with salt and pepper and pour champagne over.
Place in the oven uncovered and leave to roast for 15 minutes.
Take the salmon out of the oven and carefully pour out the champagne and juices as it's used later.
Baste the salmon with the sauce made previously and put back into the oven for another 5 minutes.
Add the champagne and fish juice to the sauce and heat through.