Mashed Potatoes with Lemon, Shallot & Rosemary Butter

In a large pot, cover the potatoes with the milk and stock. Add the rosemary sprig and 2 tsp. salt. Bring to a boil over high heat. Reduce heat to medium-low and simmer until the potatoes are tender, about 30 minutes. Remove the rosemary sprig.

Meanwhile, in a small skillet, melt 3 tbsp. butter over medium heat. Add the shallot and cook, stirring often, until translucent, 2 to 3 minutes. Add 5 tbsp. butter and stir until melted. Remove from heat. Add the chopped rosemary and the lemon zest and juice; season with salt and pepper. Cover to keep warm.

Scoop out 1 cup of the cooking liquid from the pot. Drain the potatoes and return them to the pot. Shake the pot over medium heat for 1 minute to dry the potatoes slightly.

In a small saucepan, bring the cream to a simmer over medium-low heat. Remove from heat. Add the remaining 8 tbsp. butter and stir until melted. 

Run the potatoes through a food mill or potato ricer into a large bowl. Return the potatoes to the pot. Add the hot cream mixture. Gradually stir in the reserved cooking liquid, about 1/4 cupful at a time, until the potatoes are the desired consistency; season. Transfer the potatoes to a serving dish. Using a spoon, swirl the top. Drizzle with the lemon-shallot butter. 

1 Day Ahead: Peel the potatoes and place them in a pot with the milk and stock; cover and refrigerate overnight. Make the Lemon, Shallot & Rosemary Butter; cover and refrigerate.

45 Minutes Ahead: Cook the potatoes.

10 Minutes Ahead: Reheat the butter.