Place wine, lemon juice, cream, shallots, and cream in a saucepan. Bring to a simmer over medium-high heat. Reduce heat to medium, and let simmer until liquid is reduced by about 75%, 4 to 5 minutes. Reduce heat to the lowest setting and whisk in about 2 cubes of butter. Keep butter moving until it melts. When melted, add a few more cubes, whisking continuously so butter emulsifies into the wine/lemon juice mixture.
Continue to add butter, a few cubes at a time until all of it has been incorporated and the sauce has a thick, luxurious texture, 4 to 6 minutes. Remove from heat. Taste for seasonings and add a pinch of salt and cayenne, if desired. Serve immediately.
