Cream butter and sugar until light and fluffy. Add egg yolks, one at a time, beating well after each addition. Set aside about 1/4 cup flour. Combine remaining flour and soda; add to creamed mixture alternately with yogurt, beating well after each addition. Fold in stiffly beaten egg whites. Dredge pecans in reserved flour, and fold into batter.
Spoon batter into a greased a floured 10 inch tube pan or Bundt pan. Bake at 300 degrees for 1-1/2 hours. Cool 15 minutes before removing from pan.
