Merrick's Plum Pudding Sauce

This is what was on the sheet:

"Sauce

Make a plain sauce of custard, sugar, salt, slice of butter and cold water. Guess at the amounts of each

Then flavor with French brandy "

It isn't a lot to go off of, so I found another that I used as a base.

1/2 cup unsalted butter
1 1/2 cups powdered sugar
2 tbsp French brandy
1/2 teaspoon vanilla extract

Place softened butter in a medium mixing bowl and beat until pale and fluffy. Add sugar and continue to beat until smooth. Add brandy and vanilla one tablespoon at a time. beat until combined. Cover and refrigerate the hard sauce for at least two hours, but preferably overnight. Bring to room temperature before serving.