Place a medium saucepan over medium heat and pour in the heavy cream. Bring it to a gentle boil, stirring occasionally to prevent scorching.

Once the cream starts boiling, reduce the heat to low. Add the unsalted butter and powdered sweetener, stirring well until the butter melts completely and the sweetener dissolves into the mixture.

Let the mixture simmer on low heat for 15-20 minutes, stirring constantly. During this time, the cream will reduce by about half and thicken, becoming creamy and condensed.

Remove the pan from heat and allow the condensed milk to cool for a few minutes. The mixture will thicken further as it cools.

Transfer the cooled condensed milk to a jar or an airtight container and refrigerate.