In order to make cubed beef tender, it’s essential that you sear it properly first before placing it in a low oven or slow cooker. When searing cubed beef, make sure you keep it moving so it cooks evenly on all sides. Also, use high heat and turn your cubes often so they sear evenly on all sides. If you want your cubed beef tender, don’t go above medium-high heat on your stove top or grill. Medium-high heat is also known as “medium” heat because it’s hot enough to sear but not so hot that it cooks your cubed beef quickly. It’s important to use high heat so that you can sear your cubed beef properly before putting it in a slow cooker or oven to finish cooking it.