Melt 1 tablespoon of butter and the bacon grease over medium-high heat in a large cast iron skillet. Add the potatoes. Cover with a lid and cook for about 5 minutes, stirring occasionally.
Stir in half of the diced onions. Season with salt and pepper, to taste. Cover and continue cooking, about 5 minutes, or until fork tender, stirring occasionally. Remove from the heat and place the potatoes in a large bowl, cover and keep warm.
Return to the skillet, after it has cooled slightly, and add the Velveeta. Place over medium heat, stirring until the cheese begins to melt. Stir in the cream. Continue cooking and stirring until the cheese is smooth and melted, about 5 minutes.
Stir the potatoes into the cheese until coated. Cover and keep warm.
In a medium bowl, combine the meat and remaining onion and jalapeno. Evenly form the meat into 6 patties.
In a large cast iron skillet, melt the remaining butter over medium-high heat. Place the patties in the skillet and cook for about 4 minutes per side, or until the internal temperature is 160 to 165 degrees F.
Sprinkle the potatoes with the bacon bits, plate and serve warm.