In a small bowl, combine mustard seeds and dry mustard; set aside
In a 1- to 2-quart non-aluminum pan, combine remaining ingredients. Simmer uncovered, on medium heat until reduced by half, 10-15 minutes. Pour the mixture into the mustard mixture. Let mixture soak at room temperature 24 to 48 hours; adding additional vinegar if necessary in order to maintain enough liquid to cover seeds.
Process the seeds and mixture in a blender or food processor until pureed to the texture you like (this can take at least 3 or 4 minutes).
The mixture will thicken upon standing.
If it gets too thick after a few days, stir in additional vinegar.
Melt butter in stock pot over medium heat. Cook onions until caramelized and just beginning to brown 7-10 minutes.
Add cabbage, cook for 10 minutes. Add apple, broth, bay leaf, cloves, vinegar, juniper berries, and salt. Bring to a boil, reduce heat to low, cover and simmer for 2 hours, stirring occasionally. Add more broth if needed.
Combine flour and 2 tbls broth until dissolved and stir into Rotkohl. Simmer for another minute. Add more salt and vinegar to taste.
Heat Olive Oil in medium saucepan over medium heat until shimmering. Add onion and cook, stirring occasionally, until softened but not browned, 5 to 8 minutes.
Add all other ingredients except tomato puree. stir until fragrant, about 4 minutes. Add tomato puree. Bring to a boil, then reduce heat to low and simmer, stirring occasionally, until thickened to the consistency of ketchup, 45 to 60 minutes.
Remove cardamom pods.
Transfer ketchup to blender and puree until completely smooth.
Taste ketchup and adjust seasonings if necessary. Pour ketchup into a jar, seal, and store in refrigerator for up to a month.
This Ketchup is spicy. Dip Brats, Shrimp, Pork strips, and chicken. It is delicious on scrambled eggs.