Season ground beef with salt and pepper.
Add garlic powder and thyme leaves.
Mix ingredients gently with clean hands.
Form four equal patties carefully.
Make small indents in centers.
Cook bacon until crispy golden brown.
Remove bacon and drain fat.
Sauté onions in remaining bacon fat.
Cook onions until caramelized completely.
Heat cast iron skillet over medium heat.
Add Irish butter to hot pan.
Cook patties 4 minutes per side.
Add cheese during final minute.
Toast buns lightly in pan.
Assemble burgers with all toppings.