Pierce potatoes, then microwave them for 12-15 minutes until tender. Halve, cool, remove skins, and cut into chunks.

Cook bacon in a skillet until crisp, then transfer to a paper towel-lined plate to drain and cool. Reserve up to 1 tablespoon of bacon fat and crumble the cooled bacon.

In a large pot, melt butter, then add reserved bacon fat, minced garlic, and diced onion; cook for 2-3 minutes until tender. Whisk in flour for 1-2 minutes, then slowly whisk in milk, half-and-half, and chicken stock.

Bring to a light simmer, whisk in salt, garlic salt, and pepper, then continue simmering for 5-7 minutes until slightly thickened. Stir in the remaining cheeses, bacon, and sour cream (reserving some for garnish if desired).

Remove from heat, scoop potato chunks into the pot, breaking them to your desired size. Serve hot, garnished with cheese, bacon, and chives.