Pistachio Sponge Cake

Ingredients:
1/2 cup shelled pistachios, (approximately)
1/2 cup cake flour
6 tbsp sugar
1/2 tbsp baking powder
1/4 tsp salt
1/4 cup vegetable oil
4 egg, separated
2 tbsp lemon juice
3 tbsp water
2 tsp vanilla extract
1/4 tsp cream of tartar
icing sugar, for garnish

Directions:
1. Preheat oven to 350 F.
2. Grind pistachios finely and measure 1/3 cup.
3. Sift together pastry flour, sugar, baking powder and salt. Stir in ground pistachios. Add oil, egg yolks, lemon juice, water and vanilla and beat mixture in a mixer or with electric beaters until thick, about 4 minutes.
4. Whip egg whites with cream of tartar to stiff peaks. Fold one-third of whites into batter, then remaining two-thirds. Pour batter into ungreased 10-inch springform pan (or an ungreased bundt pan) and bake for 45-55 minutes, until springy when touched.