Meanwhile, in a large, deep skillet, melt the butter. Add the shallot and cook over moderate heat until golden, about 3 minutes. Add the vodka and cook until evaporated, about 1 minute. Add 2 cups of the heavy cream and simmer over moderately high heat, stirring often until reduced by half, about 4 minutes. Stir in the salmon, season with salt and pepper and remove from heat. In a small bowl, beat the egg yolks with the remaining 1/4 cup of heavy cream.