Put oat flour, almond flour, potato starch, baking powder, sea salt and ground mustard into a medium mixing bowl. Whisk until combined and there are no clumps.
Make a little well in the middle of the mixed dry ingredients. And pour in milk and vinegar.
Slowly combine with a spoon or spatula, mix until just combined but don’t over mix. Fold in cheese if using.
Allow to sit for a few minutes, use this time to put away the ingredients, put used items in the sink and wipe off the counters.
Drop spoonfuls onto a parchment lined cookie sheet, you should get 8 biscuits.
Bake for 28-30 minutes, ovens vary but you want them crisp on the outside. You can broil for 2-3 minutes to get the browned tops if you want them. They will cook more as they cool.
Serve with butter if desired!
Notes
I measured the flours by scooping the measuring tool into the flour and then scraping the extra off with a knife. Make sure to measure the grams or use this method for more accurate results.
Be aware of the almond flour you use because some produce less fluffy results than others, I use fine grain.
You can use cashew or almond milk but the end result won’t be as rich and moist.
If mixing in cheese, use as much or as little as you prefer. I used about ¼ cup.