Pre-heat oven to 325 degrees.

Spray a 9" springform pan with non-stick spray. Cut a piece of parchment to fit the bottom; place it on the bottom of pan, spray with non-stick spray and turn coat both sides of parchment paper.

In a food processor pulse almonds until finely ground. Place in a bowl with flour and baking powder, and salt, stir to combine.

Beat egg whites until stiff, gradually adding sugar.

Add orange and vanilla extract.

Add yolks one by one, mixing well after each addition.

Gently fold in dry ingredients.

Pour batter into prepared springform pan.

Bake for 45 minutes, or until a toothpick inserted comes out clean.

Remove from oven, cool for 10 minutes before removing from pan.

Dust with powdered sugar before serving.

Garnish with sliced almonds and orange slices, optional.