Combine equal parts yellow and brown mustard seeds in a medium bowl. Pour in apple cider vinegar and enough water to fully submerge the seeds. Stir gently, then cover. Let soak for 12 to 24 hours.

In a separate bowl, mix together paprika, cayenne pepper, turmeric, and salt until evenly combined.

Transfer the softened mustard seeds and soaking liquid into a saucepan. Add the spice mixture and your choice of sweetener. Stir well.

Cook over medium-low heat, stirring for about 10 minutes until slightly thickened.

Remove from heat and blend the mixture to your desired consistency.

Cool the mustard to room temperature and transfer it into a clean jar. Refrigerate for at least 24 hours before serving.