In a saucepan, melt the butter and allulose over a very low heat.
Stir continuously until the butter begins to bubble and smell nutty. This will take about 5 minutes.
Let the mixture cook for an additional 3 minutes, while stirring continuously.
Keep stirring and slowly pour in the cream. Continue stirring until the mixture reduces. This takes about 4 minutes. The sauce should be thick enough to coat the back of a spoon.
Once the sauce has reached the right consistency, transfer it to a jar and let it cool until ready to use.