These are very thick. Very much not crepe-like. Someone thought one was a slice of bread. The sugar has been removed from the original (American) recipe on the assumption that sufficient sugar will be found elsewhere in the diet, such as from adding blueberries or whatever.
Mix the dry ingredients well.
Whisk the wet stuff together good. The buttermilk may need to be shaken before pouring. The batter with buttermilk is very thick, even moreso than for the original recipe which was for reduced fat milk. Perhaps substitute or add some water or reduced fat milk?
Mix the wet into the dry. Fold together only enough that most of the dry and wet are incorporated. Do not overmix!
Let the batter sit for 10 to 15 minutes. This is a good time to pre-heat a cast iron skillet, especially if said skillet usually lives out in a cold garage.
The optional frozen blueberries can be placed into the batter once it is on the skillet, throwing them in is pretty fun if sometimes messy. Probably you may want to defrost the blueberries first, or maybe lower the skillet temperature so the pancakes burn less before the berries are actually melted.
Note: if you use all whole grains (whole grain rye and whole grain wheat and maybe also some of the sourdough starter) then the cooking temperature will most likely need to be lowered. The whole grains appear to burn a lot easier. Also the sourdough starter should be mixed with the wet ingredients so that the gluten can be broken up there. An acid such as from buttermilk may help with this.