Roasted garlic: Preheat oven to 350 degrees F. Slice off the top of the garlic head to expose the cloves; place in center of a sheet of foil. Drizzle 1 tablespoon olive oil over the top and season generously with salt. Wrap in foil and bake in the oven until golden and tender, about 1 hour.
Potatoes: Cut peeled potatoes into ½-inch dice. (Note: Potatoes can be peeled and diced 1 day in advance. Store completely submerged in cold water in the refrigerator, changing the water every few hours to prevent browning.) Place diced potatoes into a pot filled with cold salted water (as "salty as the sea"). Bring to a boil over high heat, 6–8 minutes. Once boiling, reduce to a simmer and cook until fork tender, 15–20 minutes.
Bacon bits: In a large saucepan over medium heat, cook the bacon until crisp and browned, about 10 minutes. Use a slotted spoon to transfer bacon bits to a paper towel-lined plate. Reserve the bacon fat in a small bowl and set aside.
Return the pan to stove over low heat, and add just enough half-and-half to coat the bottom of the pan. Use a wooden spatula to deglaze the pan, scraping up all the browned bits (or "fond"). When small bubbles form around the edges of the pan, add the rest of the half-and-half. Stir until warmed through, then remove from heat.
Potatoes are done cooking when you can easily cut a piece in half with a fork. Drain potatoes in a colander, then add back to the pot. Turn heat to medium-low and let them dry, uncovered, stirring occasionally, 1–2 minutes. When the bottom of the pot is dry, turn off the heat: they are ready for the potato ricer. Transfer potatoes to a large bowl. Work all the potatoes through the ricer and back into the pot. Fold in half of the warm half-and-half and gently stir to combine; avoid overmixing the potatoes, which could lead to a gluey texture. Add another ½ cup of half-and-half, and stir again. Drizzle with 2 tablespoons reserved bacon fat, and stir to combine. Add more half-and-half as needed to reach desired consistency. Then season to taste with salt and pepper (keeping in mind that the bacon bits will also add salt).
Squeeze roasted garlic out of its skin into a small bowl, and use a fork to mash it into a paste. Add 1 tablespoon olive oil to thin out the paste and continue mashing. Fold the garlic paste into the potatoes and stir to distribute evenly; then add half the bacon bits and gently stir to incorporate. Season to taste with salt and pepper. Transfer to a warmed serving bowl, garnish with remaining bacon bits, and serve immediately.