The easiest way to thaw the hashbrowns is to place them in the fridge the night before you make this recipe. But if you forgot this essential step, try one of these two ways: 1. Spread frozen hashbrowns out on a parchment lined baking sheet, so they are in a single layer. Toss them around occasionally, this method takes anywhere from 20-30 minutes depending on the temp of your kitchen. 2. Or place frozen hashbrowns in a microwave safe bowl and microwave for 30 seconds, give it a stir, then continue to microwave in 15-20 second bursts. For both methods, be sure to pat dry with paper towels to absorb any water, so you don't end up mushy hashbrown casserole.