Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.

Melt 2 tablespoons of butter in a skillet over medium heat, then add the finely diced yellow onion and sauté for about 4 minutes.

Add minced garlic and fresh thyme, cooking for an additional minute. Remove from heat and let cool.

In a large bowl, combine ground turkey, beaten eggs, breadcrumbs, parsley, salt, pepper, and Worcestershire sauce. Fold in the cooled onion mixture carefully.

Divide the mixture into 8 portions and shape into small loaves on the baking sheet.

In a bowl, whisk together ketchup, balsamic vinegar, and brown sugar. Brush half over the loaves.

Bake for 15 minutes, then brush with remaining glaze and return to the oven for another 5-10 minutes.

Let the meatloaf rest for 5-10 minutes before serving.