Bring a large pot of water to a boil. Peel the potatoes and cut them into 1/2-inch pieces. Add the potatoes to the boiling water and cook for 20-25 minutes, or until fork tender. Drain the potatoes and return to the pot.

While the potatoes are boiling, melt the butter in a large skillet over medium to medium-high heat. Add the leeks and cook for 5 to 7 minutes or until the leeks are tender and are slightly caramelized around the edges.

Add the garlic and cook for 1 to 2 minutes, stirring constantly to prevent burning. Add the cabbage and stir to combine. Cook for another 6 to 8 minutes (stirring often), or until the cabbage has wilted a bit and is tender. Reduce heat to low and keep warm while you finish the potatoes.

Mash the cooked potatoes until almost all of the lumps are gone. Add the 1/4 cup cream to the potatoes and stir to combine. Add more cream as needed until your desired consistency is reached. (You made need more or less than 1/2 cup. It depends on how you like your potatoes.)

Pour everything from the skillet into the potatoes and stir to combine.

Season with salt and pepper to taste (you can be generous with the salt). Top with a little more butter and let it melt into the potatoes. Sprinkle the potatoes with green onion, if desired. Serve immediately