In a large mixing bowl, combine the ground beef, breadcrumbs, and egg, ensuring the egg is at room temperature for optimal blending.

Add the chopped onion and half of the BBQ sauce, mixing gently until combined, but take care not to over-mix.

Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper and shape the meatloaf mixture into a loaf form.

Bake in the preheated oven for about 50 minutes, or until the internal temperature reaches 160°F (70°C).

While the meatloaf is baking, whip up a quick barbecue sauce if you're not using a store-bought one.

In a small saucepan, combine ketchup, vinegar, brown sugar, and any additional seasonings you like. Simmer over low heat for about 10 minutes.

Heat a generous amount of oil in a skillet over medium heat. Add thinly sliced shallots to the hot oil, frying them until golden brown.

Once the meatloaf is fully cooked, allow it to rest for about 10 minutes, then slice the meatloaf thickly.

Layer each brioche bun with slices of the juicy meatloaf, drench generously with BBQ sauce, add crispy bacon, and top with fried shallots.

Present your BBQ meatloaf burgers hot and fresh, ready to be devoured!