Prepare the Peppers: Remove the stems from the hot peppers. For a milder flavor, you can remove the seeds as well.
Blend the Peppers: Place the peppers in a blender or food processor and pulse until finely chopped.
Combine Ingredients: In a medium saucepan, combine the chopped peppers, mustard, sugar, apple cider vinegar, water, cornstarch, and salt. Whisk until smooth.
Cook the Mixture: Bring the mixture to a boil over medium heat, stirring constantly. Reduce the heat and simmer for about 5 minutes, or until the mixture thickens.
Cool and Store: Remove from heat and let cool. Transfer to sterilized jars or airtight containers. Store in the refrigerator.