Place the peeled and halved potatoes in a medium pot, cover with cold water, and season generously with salt.

Bring to a boil over high heat, then reduce to a simmer and cook until the potatoes are fork-tender, about 25-35 minutes.

While potatoes cook, preheat your oven to 450°F (230°C).

Drain the cooked potatoes thoroughly and return them to the pot; mash with a potato masher until smooth.

In a microwave-safe cup, warm the whole milk for about 40 seconds until warm.

Add the butter to the mashed potatoes, stirring until melted, then stir in the minced garlic.

Add 2/3 cup of warm milk and stir; add more warm milk if needed to reach your desired consistency, then season with salt and pepper to taste.

In a medium pan over medium heat, cook the cubed smoked sausage for 2-3 minutes until nicely browned.

Add the frozen corn to the pan with the sausage and cook for another few minutes until the corn starts to get some color.

Transfer the sausage and corn mixture to the mashed potatoes and mix everything together well.

Spoon the mashed potato mixture into a medium ovenproof casserole or baking dish.

Top evenly with shredded mozzarella and grated Parmesan cheese.

Bake in the preheated oven for about 20 minutes, or until the cheese is golden brown and bubbly.

Allow the casserole to cool for 10 minutes before serving.