In a blender, pulse the chimichurri ingredients until everything is finely minced and combined.
Stream in the oil and red wine vinegar.
Make the Butter
Mash the softened butter with a fork or a blender.
Mix in 2 to 3 tablespoons of the chimichurri.
Spoon butter onto wax paper and roll up, using your fingers to shape the butter into a log if desired.
Place in fridge to set for 2 to 3 hours.
Make the Burgers
Prep your charcoal and get the grill set and ready to go.
Mix the ground beef with the salt and pepper in a large bowl. Form 8 thin patties.
Arrange a dollop of chimichurri butter in the center of 4 of the patties.
Press the other 4 patties on top and seal.
Grill the burgers to your desired doneness, the butter will be oozing out.
Place onto buns dressed with lettuce and red onion.
Slice a bit more chimichurri butter and allow to melt down and over the burgers. Serve quickly and enjoy.
The chimichurri butter can be made 2 to 3 days ahead and stored in wax paper wrapped tightly in plastic wrap in the refrigerator. Use any leftover butter on steaks, toast, or even melted over hot pasta.