Add potatoes to a large pot, cover with cold water, add salt and bring to a boil. Cook until fork tender, drain and allow excess water to evaporate. With a ricer, rice the potatoes to get rid of any excess lumps.

Heat the milk in a small pot on medium-low and, once warm, add the butter. Remove from heat and add the milk and butter mixture into the potatoes, along with the garlic and sour cream. Add a healthy dose of salt and pepper, and mix well.

Heat olive oil over medium heat in a cast iron skillet or large frying pan. Once hot, add the Brussels sprouts. Season with salt, and spread into an even layer on the pan.

Once the Brussels sprouts are golden with some crispy texture, add 1 teaspoon lemon zest, the red pepper flakes and the balsamic vinegar. Stir to combine, and allow to cook for 2–3 additional minutes, then remove from heat.

Spoon the mashed potatoes into a large serving bowl. Make some small, 1”-thick wells around the perimeter of the potatoes, and sprinkle in the Brussels sprouts. Add toasted pine nuts atop the sprouts, and sprinkle with remaining lemon zest, salt, pepper and a drizzle of olive oil. Serve immediately.