Preheat the oven to 350°F and place a rack in the lower third. Line a baking sheet with parchment paper.
In a large bowl, whisk together the almond flour, psyllium husk powder, baking powder and salt until very well combined.
Add the egg whites and apple cider vinegar. Beat with a hand mixer until the mixture is thick and crumbly.
Pour in the boiling water while mixing, and beat for about 30 seconds until the dough comes together and feels like soft modeling clay. Stop as soon as it is combined, since overmixing can make the bread dense.
With wet hands, divide the dough in half and shape each piece into a baguette about 10 inches long. Place them on the baking sheet with plenty of space between them and make 4 shallow diagonal scores across the top of each.
Bake on the lower rack for 45-50 minutes, until the crust is firm and golden and the baguettes sound hollow when tapped on the bottom.
Cool completely on a wire rack before slicing so the inside can finish setting.