Preheat oven to 325 degrees. Butter and flour a 10 inch bundt pan. In a single layer, toast pecans until fragrant about 15 minutes. Cool to room temperature and grind finely. Set aside. Turn oven to 350 degrees. In a large bowl, cream butter and sugar. Add vanilla, beat 30 seconds. Add egg yolks and beat well. Sift flour, baking powder and salt in a second bowl. In another bowl, combine pecans and half and half. Add dry ingredients to butter mixture, beating well. Then pecan mixture. Whip egg whites with an electric mixture until stiff peaks form. With a spatula fold 1/3 beaten whites into the batter, then fold in the rest. Pour batter into the pan. Bake for 1 1/2 hours until toothpick come out clean. Let cool 15 minutes and serve.