Combine ketchup, brown sugar, Dijon mustard, apple cider vinegar, Worcestershire sauce, garlic powder, and black pepper in a saucepan and stir to blend.
Heat over medium heat, stirring occasionally, until sugar is dissolved and mixture begins to bubble.
Reduce the heat to low and simmer for 10 minutes, stirring occasionally.
Allow the glaze to cool and thicken before applying it to the meatloaf.
Apply the glaze to the meatloaf using a silicone brush.
Notes
Store leftover glaze in the refrigerator for up to a week, or freeze for longer storage. Reheat gently before using.