Preheat oven to 200°F. Arrange bread slices on baking sheet and bake for 10 minutes or until lightly toasted. Tear bread into pieces and pulse into breadcrumbs using a food processor. Transfer breadcrumbs to baking sheet and toast in oven again for 5-6 minutes.
Preheat oven to 350°F. Pulse ham in batches in the food processor until finely ground. In a large bowl, combine ham with ground pork, milk, breadcrumbs, egg, ¼ cup brown sugar (packed), 1 tablespoon ground mustard, and salt, until just mixed. Shape into 1-inch balls; arrange in a single layer on greased 15×10-inch rimmed baking pans. Should make about 6 dozen balls.
Tip: Start with lower quantities of both the milk and the breadcrumbs. If mixture appears too wet, add more breadcrumbs; if mixture appears too dry, add more milk.
Prepare glaze: stir remaining (1 cup) brown sugar, ¼ cup vinegar, and remaining (1 tablespoon) ground mustard in a small saucepan and cook over medium heat until sugar is dissolved. Spoon over ham balls.
Bake until ham balls are just beginning to brown, 30-35 minutes, rotating pans and carefully stirring halfway through. Gently toss in glaze. Serve warm.
Recipe adapted from: www.tasteofhome.com