Can Yukon gold potatoes that froze in my refrigerator be used? After they thawed, they are quite mushy. Afraid to use them. Thought about using them for mash potatoes.

Potatoes in this regard that have inadvertently frozen unfortunately cannot be used. The water in the potato cells within will break down the solids and will indeed, be mush and will not perform once thawed. Potatoes should be stored cool (45 degrees or at room temperature is best) but not refrigerated, and especially not frozen. Attached is a handy infographic on the topic.