In a medium saucepan, combine unsalted butter, whole milk, and heavy whipping cream. Heat over low flame, stirring gently until the mixture is just warm to the touch, about 5 minutes.

In a large frying pan, add thickly sliced bacon over medium heat. Cook for 5-6 minutes until crispy and golden brown. Remove and set aside.

Sauté thinly sliced leeks in the same frying pan with bacon fat over medium heat for 3-4 minutes until softened.

Add thinly sliced savoy cabbage to the pan with the leeks. Season with salt and cook for 6-7 minutes until wilted and tender.

Boil a large pot of salted water, add the peeled and thinly sliced Russet and Yukon Gold potatoes. Boil for 5-7 minutes until fork-tender.

Transfer drained potatoes to a bowl and mix in the warmed dairy mixture and green onions. Fold in sautéed cabbage and crispy bacon bits.

Season with salt and ground white pepper to taste. Serve immediately, garnished with extra green onions if desired.