Preheat oven to 350 F. Prepare pan (a 10X15 pan with sides works best) with oiled parchment paper or a silicone mat.

Mix dry ingredients well -- a whisk works well. Add wet to dry, and combine well. Make sure there aren't obvious strings of egg white hanging out in the batter. Let batter set for 2 to 3 minutes to thicken up some (leave it too long and it gets past the point where it's easy to spread.)

Pour batter onto pan. Because it's going to tend to mound in the middle, you'll get a more even thickness if you spread it away from the center somewhat, in roughly a rectangle an inch or two from the sides of the pan (you can go all the way to the edge, but it will be thinner).

Bake for about 20 minutes, until it springs back when you touch the top and/or is visibly browning even more than flax already is. Cool and cut into whatever size slices you want. You don't need a sharp knife; I usually just cut it with a spatula.