Preheat oven 350°F. Spray two 8 in. round pans with vegetable pan spray.
In food processor, pulse 2/3 cup toasted pecans with 2 tablespoons flour until finely ground. Do not over grind or the pecans will turn into an oily paste.
In large bowl, whisk together ground pecans, remaining flour, sugar, baking powder and salt until well combined. Add melted butter, egg yolks, cold water, lemon extract and zest; beat with electric mixer on medium speed until smooth, about 2 minutes; set aside.
In separate large bowl, beat egg whites and cream of tartar with electric mixer until stiff peaks form. Fold 1/3 of whipped egg whites into the flour and yolk mixture to lighten. Gently fold in remaining egg whites until nearly combined. Add remaining 1/3 cup chopped pecans and gently fold until completely blended. Do not stir or beat mixture. Pour into prepared pans.
Bake 33-35 minutes or until a toothpick inserted in center of the cake comes out clean. Allow the cake to cool for 10 minutes; loosen sides gently and remove from pan to cooling grid. Cool completely.