Combine mustard seeds, wine and vinegar in a small bowl. Cover and let sit at room temperature for 48 hours.
Pour mustard seed mixture into the bowl of the food processor and grind until thick but still grainy, about 3 to 5 minutes. Add birch syrup and salt, and pulse to combine. Add spruce tips and pulse until tips are thoroughly minced.
Pour into a dry, sterilized glass jar and refrigerate. Use within two months.
Notes
Note: the mustard seeds marinate in wine and vinegar for 48 hours before you make the mustard.