Bring a large pot of salted water to a boil. Add the potatoes, reduce to a simmer and cook until the potatoes are easily pierced with a fork, about 20-30 minutes.  Drain once cooked and mash with a ricer or potato masher until smooth. Prepare the cauliflower while the potatoes are cooking.

While the potatoes are cooking, place a steamer insert into a large saucepan and fill with water to just below the bottom of the steamer. Bring the water to a boil. Add the cauliflower, cover, and steam until tender, about 15 minutes. You can alternately chop up the cauliflower and boil it in a saucepan if you don't have a steamer basket.

Once steamed, drain the cauliflower and transfer it to a food processor. Add the softened butter and garlic cloves and blend on high until smooth.

While the cauliflower and potatoes cook, dice the bacon. In a medium frying pan on medium heat, cook the bacon for about 10 minutes or until it is crispy and cooked through, stirring occasionally. Remove from pan and set aside.

Preheat the oven to broil. Combine the mashed potatoes and pureed cauliflower in a large bowl and stir together. Add the sour cream, half of the cheddar cheese, and half of the green onions. Stir to combine and add salt and pepper to taste.

Transfer the mashed potato mixture into an oven safe baking dish(s) (9x9" or similar size), top with the remaining cheese and broil until the top is melted and golden. Garnish with the extra crispy bacon bits and remaining green onions before serving.