Dear future me:
Do not attempt to mash under cooked potatoes. Counter to your time saving intuition, this will actually increase your cooking time (and frustration) 4 fold. You will be cursing at yourself for your foolishness, and then you will be making a mess in trying to fix your lumpy mass of a mess.
Also: find your ricer. I doubt the kitchen gremlins have actually stolen it. And/or buy a potato masher. Pastry cutters are are subpar for the task at hand.
Damn rice eating ancestors for not teaching me how to mash potatoes!