Preheat your oven to 400°F.
Heat oil in a large skillet over medium heat.
This part is crucial to achieve the perfect texture.
Add ground beef or lamb to the skillet.
Cook until the meat is nicely browned and crumbled.
Once it’s done, remove the meat from the pan and set it aside.
In the same pan, sauté chopped onions, minced garlic, and sliced mushrooms until they become tender and fragrant.
This should only take about 5 minutes.
Add tomato paste, beef broth, and Worcestershire sauce to the pan.
Bring the mixture to a simmer and let it thicken slightly.
Season with salt and pepper to your preference.
Pour the meat and vegetable mixture into a buttered casserole dish.
Spread mashed potatoes evenly over the top, reaching the edges.
Bake the shepherd’s pie in your preheated oven for about 30 minutes or until you see it’s hot and bubbly.
You should also ensure the potatoes are slightly golden on top.
Remove your pie from the oven and let it cool for a few minutes before serving.