Heat up a large cast iron skillet with 2 to 3 tablespoons of cooking oil such as avocado oil or olive oil to medium-high heat. Place the meat on the hot skillet in a single layer (this may take two batches depending on the size of your skillet). Allow the meat to brown for 2-3 minutes before flipping it to the other side and allowing it to brown for another minute or two, or until there is a nice golden brown crust on two sides. Transfer the meat to a plate and repeat this process for the remaining beef. Once the meat is browned, transfer the meat to the crock pot.