Mix ground beef, cracker crumbs, onion, egg, milk, garlic, kosher salt, and black pepper in a large bowl until evenly blended. Shape meat mixture into twelve 3-inch patties about 1 1/4-inch thick.
Heat vegetable shortening in a large skillet over medium-high heat. Sear patties until golden brown, about 2 minutes per side. Reduce heat to low and continue cooking, uncovered, until patties are no longer pink in the center, about 20 minutes more. Remove patties from skillet and drain on paper towels until ready to serve.