I would guess sour cream or creme fraiche (less tangy), or even buttermilk.

As for the mascarpone, oh ho, so much you can do.

A good one for that amount might be to make some polenta or grits and stir it in at the end. That makes a delicious side for which to pile on vegetables.
I'm assuming you don't want to do a tart, but it's always great slightly sweetened and flavored with either zest or coffee, vanilla, etc., whipped with some cream, and put into a tart shell with some fruit to finish.
A creamy pasta.
Stirred into risotto.
Topping for baked/grilled fruit
Mac and cheese

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