Preheat oven to 350°F. In a large bowl, combine ground ham, ground pork, crushed Corn Chex, brown sugar, mustard, salt, milk, and egg until just combined.
Roll mixture into 1-inch balls and place in a single layer on a rimmed baking sheet.
In a small saucepan over low heat, combine glaze brown sugar, apple cider vinegar, and mustard. Stir 3 to 4 minutes until smooth.
Pour warm glaze over ham balls. Cover pan tightly with foil and bake 20 minutes.
Remove foil and bake 20 more minutes, until glaze caramelizes and ham balls reach 160°F.
Transfer to a serving dish and gently toss with glaze from the pan. Serve hot.
Notes
Do not overmix the meat mixture or the ham balls can turn tight. Keep the balls about 1 inch so they cook evenly. Use a rimmed pan because the glaze pools as it bakes. Cover for the first half of baking to keep the centers moist.