Preheat the oven to 425°F. Line a half-sheet pan with parchment paper and set aside. Remove the kielbasas from the packaging and dry them with paper towels. Straighten the kielbasas and cut them in half; you should have four 8-inch pieces.
Place one piece on a large cutting board between two chopsticks. Using a ruler as a guide, cut the kielbasa into ¼-inch slices with a large kitchen knife, making sure to stop at the chopsticks so you do not cut all the way through. Remove the chopsticks and ruler, then cut the sliced kielbasa into bites with three rings each. Place the bites in a large bowl and repeat slicing and cutting the remaining kielbasa.
In a small bowl add the stone ground Dijon mustard, apple cider vinegar, Worcestershire sauce, and light brown sugar. Whisk everything together until well combined, this makes about one cup.
Remove about half of the mustard sauce, about ½ cup, and place it in another small bowl. Add the mayonnaise to one of the bowls of mustard sauce. Whisk to combine the mayonnaise with the sauce to make the mustard dip, and place in the refrigerator until ready to use.
Pour the remaining half of the mustard sauce over the kielbasa bites in a bowl. Stir the bites to coat them in the mustard sauce. Use the spatula to rub the mustard sauce in between the slices, then place the mustard-coated bites on the prepared sheet pan, sliced sides up. Bake in a 425°F oven for 25 to 30 minutes, until crispy.
Once the desired crispiness is reached, remove the pan from the oven. Serve warm with the mustard dipping sauce.
Yield 40 bites.