Preheat oven to 350. Butter and flour a 9 inch tube pan. Mix flour, baking powder, baking soda, and salt in mixing bowl. Beat eggs and sugar in large mixing bowl with mixer on medium speed til light. Beat in vanilla and oil. Gradually add flour mixture on low speed, then add yogurt and mix til blended. Pour batter into pan to about one third full. To make the walnuts, mix the sugar, cinnamon, and walnuts in mixing bowl. Sprinkle ¾ of the walnuts over batter in pan and pour in remaining batter. Sprinkle with remaining walnut mixture. Bake for 50 to 60 minutes or til a tester inserted in center comes out clean. Cool in pan for 20 minutes then transfer to a rack to cool for 1 hour. Set cooled cake on serving plate and top with icing.
3 cups powdered sugar, plus more if needed
3 Tbsp. warm water
2 tp. Vanilla extract
Put sugar in medium bowl and gradually beat in water til smooth. Beat in vanilla if needed, add more sugar.
Pic and recipe courtesy of Pioneer Woman