Water roux for recipe that doesn't have water?
I'd like to modify an existing sweet bread recipe to use the water roux technique. The general guideline I've found is to take 10% of the flour and add water that's 5x the amount of flour. That's easy enough for recipes that have water. The sweet bread recipe that I have uses only milk. How do I use the water roux technique? My ideas:
1. Use milk instead of water
2. Use water, and reduce the milk accordingly
Which option is correct? Or is there a different approach?