Melt 4 tablespoons of unsalted butter over low heat in a small pot. Add 1 cup of whole milk and 1/2 cup of heavy whipping cream, stirring continuously until warmed through—about 5 minutes.

Cook 6 slices of sliced bacon in a large skillet over medium heat until crispy, about 6-8 minutes. Remove bacon and drain on a paper towel-lined plate, leaving 2 tablespoons of bacon fat in the pan.

Add 1 sliced leek to the skillet using the bacon fat. Sauté over medium heat for 3-4 minutes until soft and fragrant, scraping any brown bits from the bottom.

Add 4 cups of chopped savoy cabbage and a pinch of salt to the skillet with leeks. Cook, stirring frequently for about 6-7 minutes until wilted and soft.

In a large pot, bring salted water to a boil. Slice 2 pounds of Russet and Yukon Gold potatoes and add them. Cook for about 5-7 minutes or until fork-tender, then drain well.

Quickly add chopped green onions to the warm milk mixture in the pot and let it infuse for 1-2 minutes. Pour this mixture over the drained potatoes for mashing.

Mash the drained potatoes until smooth with no lumps. The warmth will help combine all ingredients seamlessly.

In a large mixing bowl, combine the mashed potatoes with sautéed cabbage and leeks, crispy bacon, and season with salt and white pepper. Fold in the warm milk mixture until incorporated.