Preheat oven to 325°F. Place 1 egg white into a medium sized bowl along with the maple syrup and ¼ teaspoon of salt and beat on high with a hand mixer for a couple of minutes until the mixture turns light and fluffy. Add the vanilla extract and almond extract and beat just to combine. Start adding the almond flour, ½ cup at a time, and use a spatula to fold it into the mixture. Once all the flour is incorporated, let the dough rest for 15 minutes, so the almond flour can hydrate. The mixture will be soft and very sticky.
Chop up the sliced almonds into smaller pieces and set aside. Whisk the second egg white, and set it aside. Dip your hands in water and using a cookie dough portion scooper (that is about 1.5 tablespoons in size) or a spoon, scoop some dough and form it into a ball. The water will prevent the dough from sticking to your hands. Dip the dough ball into the whisked egg white, and then roll it into the chopped up sliced almonds. The egg white will help the almond pieces stick.
Place the balls onto a sheet tray lined with parchment paper. Bake at 325°F for about 30-35 minutes until they are deep golden brown around the edges. Let cookies cool on a wire rack. Store cookies in a cool dry place.