Hearty Beef and Mushroom Shepherd's Pie with Rosemary Potato Crust

Peel the russet potatoes and cut into 1-inch chunks. Place in a large pot and cover with cold water. Add 1 teaspoon salt and bring to a boil. Cook until fork-tender, about 15 minutes.

While potatoes are cooking, dice the onion, slice the mushrooms, mince the garlic, and dice the carrots and celery into small pieces.

Preheat oven to 375°F (190°C).

In a large skillet or Dutch oven, brown 1 lb ground beef over medium-high heat, breaking it up with a wooden spoon, about 5 minutes. Season with salt and pepper.

Add the diced onion, carrots, and celery to the beef. Cook for 5 minutes until vegetables begin to soften.

Add sliced mushrooms and minced garlic to the skillet. Cook for another 3 minutes until mushrooms release their moisture.

Stir in 2 tbsp tomato paste and cook for 1 minute until it darkens slightly.

Sprinkle 2 tbsp flour over the mixture and stir to coat everything evenly.

Add 1 cup beef broth and 1 tbsp Worcestershire sauce, stirring to combine. Bring to a simmer and cook for 5 minutes until the sauce thickens.

Stir in 1/2 cup frozen peas and remove from heat. Taste and adjust seasoning with salt and pepper as needed.

Drain the cooked potatoes and return them to the pot. Add 4 tbsp butter and 1/3 cup milk. Mash until smooth and creamy.

Finely chop 1 tbsp fresh rosemary and fold into the mashed potatoes. Season with salt and pepper to taste.

Transfer the beef mixture to a 9x13 inch baking dish, spreading it evenly.

Carefully spoon the rosemary mashed potatoes over the beef mixture, then use a fork to create texture on the surface.

Bake in the preheated oven for 25-30 minutes, until the top is golden brown and the filling is bubbling around the edges.

Let stand for 5 minutes before serving.