How to Make It
Preheat the oven to 350°. Bring a large pot of water to a boil. Add the onions and cook for 5 minutes. Drain and rinse under cold water. Use a sharp knife to trim off the root ends, then pinch the onions to remove the skins.
In a medium, deep skillet, cook the bacon over moderately high heat until the fat is rendered, 3 to 4 minutes. Pour the bacon fat into a heatproof cup and reserve 1 1/2 teaspoons. Drain the bacon on paper towels.
Add the butter to the skillet along with the shallots and garlic. Cook over moderate heat, stirring, until softened, about 3 minutes. Add the cream and simmer until reduced by half, about 10 minutes; season with salt and pepper. Transfer the pearl onions to a large, shallow baking dish and cover with the cream.
In a small bowl, toss the panko with the bacon, parsley and the 1 1/2 teaspoons of reserved bacon fat. Season lightly with salt and pepper. Spread the crumb mixture over the onions and bake until the crumbs are toasted and the onions are bubbling, about 30 minutes.