u003cbr/u003ePeach cobbler recipes made with canned peaches tend to be runnier than when using fresh or frozen peaches. But the longer the peach cobbler cools, the more it will thicken up. However, if you would like to prevent it from being runny in the first place, you can add cornstarch to the filling mixture. Take 1-2 tablespoons of cornstarch and mix with 1-2 tablespoons of water. Then add this slurry to the filling before cooking.