Preheat oven to 325°F.
On a baking sheet, toast the pecans until fragrant, about 15 minutes. Cool to room temperature and grind finely in a nut grinder. Set aside.
Adjust oven heat to 350°F.
In large mixing bowl, cream butter and sugar at medium speed until light and fluffy. Add vanilla and beat another 30 seconds to incorporate. Add egg yolks, one at a time, beating well after each addition.
Combine the ground pecans and half and half, stirring to moisten thoroughly. Add ⅓ of dry ingredients to butter mixture and beat to incorporate well, then add ⅓ of the pecan mixture and beat well. Repeat, alternating thirds of the dry ingredients and the nut mixture and scraping down sides of the bowl as necessary, until all has been added.
Whip egg whites until stiff. With a spatula, gently fold about ⅓ of the beaten whites into the batter, then fold in the rest.
Butter and flour a Bundt pan; pour in the batter. Bake at 350°F for 1½ hours or until a toothpick inserted in the center comes out clean. Begin checking for doneness after 1 hour.