Preheat oven to 375F (190C).

Peel and cut potatoes into 1 ½” (4cm) pieces. Place in a colander and rinse under cold water for one minute.

Transfer potatoes to a large pot, cover with at least an inch of water, and generously salt the water. Place pot on stovetop over high heat and bring to a boil, stirring occasionally. Once potatoes are fork-tender, carefully drain potatoes into colander then return to the pot and allow to sit for a minute (this helps the excess water evaporate from the pan).

Add milk, butter, sour cream or cream cheese, garlic, salt, and pepper,and mash until potatoes reach desired consistency. Stir well.

Stir in 1 cup (4oz) or shredded cheddar cheese until well distributed.

Spread potatoes into a 2 or 2.5 qt casserole dish. Top with remaining ½ cup (2oz) of shredded cheddar cheese and crumbled bacon.

Lightly butter a large piece of foil and lightly cover the casserole dish (buttered side down). Transfer to center rack of 375F (190C) preheated oven and bake for 20 mins, remove the foil, and continue baking for another 15-20 minutes, until cheese is melty and bubbly.

Remove from oven and top with chives or scallions. Serve warm.