Preheat your oven to 400°F (200°C). Scrub the potatoes thoroughly under running water. Pat them dry with paper towels, then prick each potato several times with a fork.
Brush each potato with olive oil and sprinkle lightly with coarse salt. Place them directly on the middle rack of your preheated oven and bake for 45-60 minutes until the skin is crispy and the inside yields easily when pierced with a fork.
Allow the baked potatoes to cool for about 10 minutes. Cut each potato in half lengthwise. Using a spoon, carefully scoop out the potato flesh, leaving about 1/4 inch of potato attached to the skin to maintain structure.
Place the scooped potato flesh in a large mixing bowl. Add the softened butter and use a potato masher or fork to combine until the butter melts completely.
Add the sour cream and warmed milk to the mashed potatoes. Mix until smooth and creamy, being careful not to overmix.
Fold in 1 cup of the shredded cheddar cheese, chopped chives, minced garlic, salt, and pepper.
Spoon or pipe the potato mixture back into the potato skins, dividing it evenly among all the halves. Create a small well in the center of each filled potato half.
Sprinkle the remaining 1/2 cup of cheddar cheese on top of each potato. If using bacon, sprinkle the crumbled pieces over the cheese.
Place the stuffed potato halves on a baking sheet and return to the oven for 15-20 minutes, until the cheese is bubbly and beginning to brown.
Remove from the oven and let cool for 5 minutes. Garnish with additional fresh chives and a small dollop of sour cream if desired. Serve while still warm.