What I do, and I double checked as well. I whip the cream once and place it in the refrigerator.
After an hour some milk will separate out. I then skim the cream off this and whip it again with a little vanilla and sugar. This then thickens up nicely. I got this tip from a book written by Louis Diat, French Cooking for Americans. 1946.

try it with about 4-6 drops of angostura bitters to smooth out the bite

making violet mustard isn't difficult but it is time consuming:

2 cups red wine
2 cups port
2 cups black grapes

boil slowly for approx 1 hour
then strain

add 4 ounces dry mustard (i use coleman's brand to avoid bitterness) smoothed in 1/4 to 1/2 cup cold water or wine vinegar [ or you can use 1 cup dijon mustard ]
and 1 cup whole grain (deli style) mustard

stir to incorporate ingredients well

put back on low heat to reduce (or use a double boiler) and stir until you get the right consistency