Preheat your oven to 350 degrees F. Grease a casserole dish and set aside.
Place the potato chunks in a large pot, cover with water, and add 1 tbsp of kosher salt. Bring to a boil, then reduce heat to simmer until potatoes are tender (about 15-20 minutes).
While potatoes cook, heat a skillet over medium heat and cook the bacon until crispy. Drain on paper towels and set aside.
Drain the potatoes and return them to the pot. Add 2/3 cup of milk and the butter. Mash until smooth and creamy.