Preheat oven to 375ºF (190ºC) and line a baking sheet with parchment paper.
Combine dry ingredients in a medium-sized mixing bowl.
Grate in cold butter using a cheese grater. Toss to combine and break up any pieces that have stuck together.
Add in buttermilk and egg whites and stir well to combine.
Make biscuits by either just making them as drop biscuits and scooping the batter onto the parchment paper (you can hand shape them once they are on there too) OR if you want pretty biscuits (like in the photos) and don't mind the extra effort, you'll want to spoon the mixture into a well-greased* 1/3 cup measure, gently press the batter down into the measuring cup with your fingers, then flip it over and tap the bottom and sides until the biscuit falls out onto the parchment paper.
Bake for 20-22 minutes. This cook time is for the 1/3 cup batter biscuits. If you have made drop biscuits and they are smaller, you will likely need to decrease the cook time a bit. Biscuits are done when they have a nice golden color to them.
Allow to cool on the pan for about 5 minutes, then move to a cooling rack for them to finish cooling. Due to their delicate texture, these biscuits are best if you let them cool for at least 10 minutes before eating. I like to leave them for about 15-20 minutes.
Enjoy!
Notes
*You want to grease the 1/3 cup measure really well with avocado oil so the batter doesn't stick. And when I say really well, I mean it should drip out if you turn it over. When you try to remove the first biscuit, you'll know if you added enough or not. If it's sticking, just return the batter to the bowl, wash and dry the measuring cup, then grease it and try again. These biscuits are a little more delicate than normal biscuits, so take care when handling them, especially if you're transporting them to an event or packing for lunch.