Step by step recipe:

1. 15 min.
   Preheat the oven to 360°F (180°C).
   
   Spread 60 g mustard seeds on a sheet of cooking parchment laid on a baking sheet. Put the mustard seeds in the oven for 15 minutes to dry roast.
2. 1 min.
   As soon as you take the seeds out of the oven, tip them into 60 g water, stir briefly, then leave on one side to cool.
3. 4 min.
   Put into a mixer bowl, in the following order: 180 ml milk (straight from the fridge), 2 eggs, 100 g Soured dough, 500 g plain white flour (French Type 65), 15 g yeast, 9 g fine (or table) salt and 30 g French mustard.
4. 15 min.
   Knead on slow speed for 15 minutes.
   
   Add the mustard seeds 2 minutes before the end of kneading.
   
   
   
   Note: For the best way to knead, see: A few tips for effective kneading at home..
5. 1 hour 30 min.
   Gather the dough into a ball and transfer it to a large, clean bowl. Cover with a plastic sheet and leave for 1 hour 30 minutes.
6. 5 min.
   After this time, cut and weigh out the dough into 100 g lumps.
7. 10 min.
   Roll these into balls.
8. 2 hours
   Arrange the balls evenly spaced on a baking sheet.
   
   Cover with a plastic sheet and leave in a warm place to rest for 2 hours.
9. 25 min.
   Bake at 460°F (240°C) for about 25 minutes, until golden brown.
   
   Note: As when baking any bread, you should ensure that the oven is filled with steam for the first 15 minutes of baking. This page shows you how; it really is the secret of golden-brown, crusty loaves..
10. 
    Leave to cool on a wire rack.