Soak the seeds in water for at least two hours, for best results soak them all night long;
In a food processor blend the soaked seeds, wine and some salt and vinegar;
Use pulse blending first until the mustard separates from the seeds;
Do the seasoning as desired with the rest of salt and vinegar;
Add honey/sugar to suppress the bitterness;
Strain the whole mixture through a fine mesh (strainer) to separate the mustard from the seeds (this step takes a long time and someone can avoid it - the mustard is already good enough)
Notes
Alternatively:
for step 2 you can use a mortar, but it takes a very long time;
for step 6 you can use a medium / slow speed juicer.