In a medium bowl, combine ground beef, Italian sausage, chopped onion, salt and pepper. Using your hands, mix together and form into patties.
Cook patties on medium high heat on a grill or on a grill pan. Cook for about 16 minutes, flipping half way through cook time. Two minutes before they are done, add pepperjack cheese to patties to melt.
While burgers are cooking, prepare the gravy. Saute 1/2 pound ground sausage in a skillet. Once cooked remove from skillet and drain. Set aside
Add butter, onions, tomatillos, and jalepenos to the skillet. Cook for 6 minutes, until reduced in size. Add back the Italian sausage. Sprinkle with flour and whisk in milk, salt, pepper, cayenne, and garlic powder. Bring to a boil, then remove from heat.
To plate, slice biscuit in half. Add patty, top with gravy and other half of biscuit. Garnish with cilantro, jalepeno, and lime juice.