I got this recipe from him. It actually calls for the eggs to be separated so that the whites can be beaten and folded in at the end, to make the waffles more light, but I've found they're light enough without that extra step. I've also sometimes substituted melted butter or ghee for all or part of the oil, and I'm guessing melted coconut oil would also be a tasty option.
I make my sourdough with 100% white whole wheat flour, but my dad uses red wheat flour, and that's also good. The fermenting process helps break down the whole grain so it's a little more tender and easier to digest. It works well to feed your sourdough the night before making this so you have plenty to use and so that the sourdough isn't too sour (since this recipe doesn't call for any additional flour, I've found that if I use really ripened sourdough without feeding it first, the flavor is a little too strong).
Dad's Sourdough Waffles
2 1/2 c. sourdough
milk to thin (or buttermilk or yogurt, or water)
3/4 tsp baking soda
3/4 tsp salt
1 1/2 Tbs. sugar
1/4 cup oil (or melted butter, ghee, coconut oil)
Mix together the baking soda, salt, and sugar in a small bowl. Stir together the sourdough, eggs, and enough liquid to make it a good waffle consistency, then stir in the oil and the dry ingredients just to blend. Cook in waffle iron.
Note: it works well to freeze any leftovers and then warm them in the toaster when ready to eat them.