Preheat oven to 325 degrees Fahrenheit. Grease three (eight-inch) round pans.

Pulse pistachios in food processor until they reach a flour-like consistency.

In a bowl, combine pistachios, flour, cornstarch, baking powder, baking soda, and salt.

In the bowl of an electric mixer, cream margarine for two minutes. Add sugar and cream for an additional three minutes. Add egg and vanilla and mix until combined. Add pistachio-flour mixture, alternating with the cold water, in three separate additions. Scrape sides and continue to mix until combined.

In a clean mixing bowl, beat egg whites until stiff peaks form. Fold into batter. Divide batter into prepared pans. Bake for 40 to 45 minutes, or until a toothpick inserted comes out clean.

Meanwhile, in the bowl of an electric mixer, cream margarine for two minutes. Add confectioner’s sugar, one cup at a time. Add almond extract. Fold in chopped almonds. Set filling aside.

Pulse pistachios in the food processor until they reach a flour-like consistency.

In the bowl of an electric mixer, cream margarine. Add sugar, one cup at a time. Add vanilla and milk, and mix to combine; then add pistachios.

Once cake is cool, put almond filling in between the layers. Use pistachio buttercream to frost outside of cake.