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 and floured 10 inch tube pan or Bundt pan. Bake at 300 degrees for 1-1/2 hours. Cool 15 minutes before removing from pan.