"sweetened with" is correct and usable in written English.
It is typically used to indicate that something has been enhanced or improved with something else. For example, "The tea was sweetened with honey."
But do we really think of our coffee sweetened with an artificial sweetener as diet coffee?
Beverages sweetened with steviol glycosides were found free from other high-potency sweeteners.
They're lightly sweetened with honey, so I feel less guilty.
It is sweetened with agave and zapped with some caffeine.
It appears to be sweetened with maple syrup and just makes you wonder why.
Do I prefer pecan pie sweetened with cider or with maple syrup?
Tzimmes is a vegetable or meat dish sweetened with sugar or honey.
Pan-roasted branzino rests on a spoonful of brandade sweetened with caramelized fennel.
The fat melts into the rice which, sweetened with sultanas, creates a rich, satisfying dish.
Consider how many manufactured foods, ice cream included, are sweetened with corn syrup.
"These hard-hitting stories... are bitter but sweetened with humor," Janet Kaye wrote here in 2000.
