Dice the onion into 1/4-inch pieces, mince the garlic cloves, dice the carrots into 1/2-inch cubes, and slice the spring onions for garnish. Preheat your oven to 390°F so it reaches temperature while you build the meat sauce. Crush the bouillon cube with your fingers or a fork to help it dissolve more easily into the sauce.

Heat the grease in a large pot over medium-high heat. Once shimmering, add the diced onion and minced garlic, sautéing for 3-4 minutes until softened and fragrant. Add the ground beef and cook, breaking it apart with a spoon, until browned and no pink remains (about 5-7 minutes). Stir in the tomato puree, thyme, oregano, and paprika, allowing these spices to bloom in the fat for 30 seconds—this releases their aromatic oils and builds deeper flavor.

Add the chopped tomatoes, crushed bouillon cube, and Worcestershire sauce to the pot, stirring well to combine. Bring to a simmer, then fold in the diced carrots and frozen peas. Let this simmer for 5-8 minutes to soften the carrots slightly and allow the flavors to meld. I like to taste the sauce at this point and adjust seasoning with salt and pepper—the bouillon provides some saltiness, so season carefully. The sauce should be richly flavored and thick enough to hold its shape without being dry.

Pour the meat sauce from Step 3 into a lightly greased 9x13 inch baking dish, spreading it into an even layer. Layer the thinly sliced scalloped potatoes directly over the meat sauce, overlapping them slightly in rows for an attractive presentation. The potatoes should create an even, compact layer. Sprinkle the mozzarella cheese evenly over the potato layer—I prefer Galbani for its superior melting quality, but any good-quality mozzarella will work.

Place the assembled shepherd's pie in your preheated 390°F oven and bake for 25-30 minutes until the potatoes are tender when pierced with a fork and the cheese is melted and lightly golden. Remove from the oven and let rest for 5-10 minutes—this allows the layers to set slightly and makes serving cleaner. Top with the sliced spring onions from Step 1 and serve directly from the dish or portion into individual plates.