Separate eggs. Crack each egg into your hand and let the whites run into a bowl. Place yolks in a second bowl.
Preheat the oven to 375 degrees F (190 degrees C). Butter a loaf pan and line the bottom with parchment paper.
Place almond flour in a food processor. Add salt, baking powder, and egg yolks. Pour in melted butter. Pulse, scraping down the sides once or twice, until mixture comes together.
Sprinkle cream of tartar into the egg whites. Whisk until soft peaks form. Transfer about 1/3 of the mixture into the food processor. Pulse on and off, scraping mixture down with a spatula as needed, until well blended. Scrape mixture into the bowl with the egg whites. Fold together until well combined but still airy. Pour batter into the prepared loaf pan.
Bake in the preheated oven until golden brown and a toothpick inserted into the center comes out clean, about 30 minutes.
Run a thin knife along the edge bread and let rest for 10 minutes. Turn bread out onto a wire rack and cool to room temperature before slicing.