Place the cut potato chunks in a large pot and cover with cold water by about 1 inch. Add 1 tablespoon kosher salt. Bring to a boil over high heat, then reduce to a simmer and cook until potatoes are very tender when pierced with a fork, about 15–20 minutes depending on chunk size.

Drain and dry

Drain the potatoes in a colander for 1–2 minutes, then return them to the still-warm pot. Place the pot back on the stove over low heat for 1 minute to evaporate excess moisture, shaking the pot occasionally to avoid sticking.

Mash and finish

Add 4 tablespoons of unsalted butter to the potatoes and begin mashing with a potato masher or ricer until mostly smooth. Warm the 3 cups of milk (do not boil) and add it gradually while mashing until you reach a creamy, fluffy texture. Stir in 1 teaspoon salt and 1 teaspoon freshly ground black pepper. If using, fold in 1/2 cup sour cream for extra tang and creaminess. Taste and adjust seasoning.

Keep mashed potatoes warm over very low heat, or transfer to a warmed serving bowl covered with foil while you make the gravy.

Brown Gravy

Sweat onion and garlic

In a medium skillet or saucepan over medium heat melt 2 tablespoons butter. Add the finely diced onion and a pinch of salt and cook, stirring occasionally, until the onion is softened and beginning to brown, about 6–8 minutes. Add the minced garlic and cook 30–60 seconds until fragrant.

Make roux

Sprinkle 3 tablespoons all-purpose flour over the softened onions and stir to coat. Cook the flour-onion mixture, stirring constantly, for 2–3 minutes to remove the raw flour taste and develop a light nutty color.

Deglaze and build gravy

Optionally add 2 tablespoons dry red wine and scrape up any browned bits from the pan, cooking until most of the wine has evaporated (1–2 minutes). Gradually whisk in 2 cups beef stock, a splash at a time, until smooth. Add 1 teaspoon Worcestershire sauce, 1 teaspoon soy sauce, and 1 teaspoon fresh thyme (or 1/2 tsp dried). Bring the gravy to a gentle simmer, whisking occasionally, until it thickens to coating consistency, about 4–6 minutes.

Adjust seasoning and strain (optional)

Season with 1/2 teaspoon salt and 1/2 teaspoon freshly ground black pepper, tasting and adjusting as needed. For an ultrasmooth gravy, strain through a fine-mesh sieve into a clean saucepan, pressing on solids to extract flavor; otherwise leave as-is for a heartier texture.

Keep the gravy warm over low heat, stirring occasionally. If it becomes too thick, whisk in a little warm water or extra stock, 1 tablespoon at a time, until desired consistency is reached.

Finish & Serve

Spoon a generous portion of mashed potatoes onto plates or a serving platter. Ladle warm brown gravy over the potatoes. Sprinkle with chopped fresh parsley for color and serve immediately.