Pretty please check out the video for guidance (as you'll soon come to realize it's much easier than it sounds!) ;)
Add yeast and maple syrup (to feed the yeast, see notes) to a large bowl. Heat up water to 105-110°F, and if you don't have a thermometer it should only feel lightly warm to touch. Pour water over yeast mixture, cover bowl with a kitchen towel and allow to rest for 7 minutes. The mixture should be bubbly, if it isn't start again (too cold water won't activate the yeast and too hot will kill it).
Mix your flours while the yeast is proofing. Add almond flour, psyllium husk, xanthan gum, baking powder and salt to a medium bowl and whisk until thoroughly mixed. Set aside.
Once your yeast is proofed, add in the egg, egg whites, olive oil and vinegar. Mix with a whisk or electric mixer for a couple minutes until light and frothy. Add the flour mixture in two batches, mixing until thoroughly incorporated. You want to mix thoroughly and quickly to activate the xanthan gum, though the dough will become very thick by the end and form into a round.
Line a 10-inch skillet or dish with parchment paper and grease with olive oil (so the dough doesn't stick while you spread it). Dip a spatula (or your fingers) in water and spread the dough until even in thickness. With your fingers wet, make indentations in the dough. Fill some of the indentations with rosemary springs and some more on top, follow with a generous drizzle of olive oil and some flakey sea salt. Cover with a kitchen towel and place in a warm draft-free space for about an hour until lighter in texture. You don't want the dough to double, but it will puff up noticeably (see pictures for reference).
Preheat oven to 350°F/180°C while the dough is proofing. And if you're baking at high altitude, you'll want to bake it at 375°F/190°C.
Transfer the skillet gently into the oven and bake for 25-30 minutes, covering with a foil dome at minute 10 to avoid excessive browning. Just be sure that the foil isn't resting directly on the focaccia (i.e. we rest it over the edges of the parchment paper).
Allow the focaccia to cool completely for best texture, as the bread will continue to cook while cooling resulting in a better crumb. But if you can't hold your horses, at least give it 15 minutes before digging in (just note that texture will not be ideal, so we prefer to wait even if we have to reheat!).
Keep stored in an airtight container at room temperature for a couple days, giving it a light toast before serving again.
*Before you scream sugar (!!) remember that the yeast will feed on such sugar to emit carbon dioxide, so it doesn’t affect the carb count much (if at all). And yes, this is a scientific fact. Or just buy some inulin (fully keto, but I know most peeps don't have it in their kitchens). **Using ground flax seeds instead of xanthan gum will result in a slightly denser crumb. But the results will be equally delicious.