Cook rice. Cook the rice for about 12 minutes, just until it begins to soften. Do not overcook, as the rice will finish cooking in the oven. Drain and rinse under cold water, then transfer to a large mixing bowl. The rice will not be fully cooked.
Cook onions. Meanwhile, sauté the onions in 2 tablespoons of butter over medium-high heat until softened.
Cook carrots. Clean and grate the carrots. Add them to the onions along with the remaining 2 tablespoons of butter. Cook until the carrots are tender. Remove from the heat and allow the vegetables to cool slightly.
Mix up filling. In a large bowl, combine the rice, ground meat, sautéed vegetables, seasonings, dill, mayonnaise, and minced garlic. Mix until well combined.
Cut cabbage leaves. Once the cabbage leaves have cooled, trim away the thick center rib from each leaf. Depending on the size, cut the leaves into 2 or 3 sections.
Prep baking dish. Line the bottom of a roasting pan or casserole dish with any unused cabbage leaves.
Build rolls. Take a section of cabbage leaf and place a portion of the meat mixture in the center. Shape the filling into a small cone. Fold the sides of the cabbage around the filling, leaving the top slightly open.
Stack cabbage rolls. Place the cabbage roll seam-side down in the prepared baking dish. Repeat with the remaining filling and cabbage leaves until you have a complete layer.
Garnish. Remove the seeds from the red pepper and slice it into thin strips. Scatter half of the pepper strips over the cabbage rolls and top with half of the butter, cut into small pieces.
Continue layering rolls. Add the remaining cabbage rolls in a second layer. Top with the remaining pepper strips and the rest of the butter.