Take a bowl and place a sieve on top. Open the oysters above the sieve and catch the juice and the oysters. Clean the shells. Place them on a plate. Check that no pieces of shell are left on the oysters.
Strain the juice and add an equal amount of champagne. Pour into a saucepan and let it reduce by half. Season with pepper and salt and whisk in the sour cream. Bring to a brief boil and remove from heat.
At the end, briefly add the oysters to the sauce and gently mix them in. Distribute them in the shells on a plate.
Finely chop the endive and add it to the sauce. Let it cook for 2 minutes until the leaves are soft.
Distribute spoonfuls of sauce and endive on the shells and finish with salmon roe.