Tips to prevent the mashed potato topping from becoming soggy during baking:
Ensure the filling is not too watery. Make sure to cook the liquid down before transferring the meat mixture to the casserole dish. Cool the filling before adding the mashed potatoes. This helps create a barrier between the filling and the mashed potatoes, reducing the chances of moisture seeping through. Spread the mashed potatoes evenly. This creates a sealed layer that helps prevent moisture from penetrating the potatoes. Use a thicker layer of mashed potatoes. This provides additional insulation for the filling, helping to keep it from making the potatoes soggy.