Preheat the oven to 350 degrees.
Line a the bottom of a cake pan with parchment paper. Grease the sides of the pan.
Measure out gluten-free flour, baking powder, and salt into a small bowl and set aside.
In a separate bowl mix oil, egg yolks, sour cream, applesauce, and vanilla. Slowly stir in the sugar and mix until combined.
Add the flour mixture to the batter.
Using the whisk attachment, beat the egg whites and one tablespoon of sugar until stiff peaks form.
Gently fold the cake batter into the egg whites until thoroughly mixed. Folding in a third of the batter at a time.
Pour the batter into the prepared cake pan.
Bake for about 32 minutes until an inserted toothpick comes out clean.
Cool in the pan for 10-15 minutes.
Turn out onto a wire rack and cool completely.