I've answered several topics on this in several threads, figured I'd gather it all together.
5 parts cream to 3 parts mascarpone; whipped together to semistiff peaks.
This may be frozen for an ice cream substitute. Any number of flavoring agents can be added and any number of versions can be made. Sky's the limit. If it makes it to the table, I dip berries in it. If you mix the berries into it, it makes a great fruit salad. I've heard of people using cream cheese instead of mascarpone; that's also tasty, just slightly more savory.