Pre-heat oven to 350° (180° celsius), grease & flour a 10" (4 liter) tube/bundt pan.
In a small bowl combine the sugar, cinnamon and walnuts.
In a medium bowl whisk together the flour, baking powder, baking soda and salt.
In a large bowl cream the butter and sugar at medium speed until fluffy 2-3 minutes, add the eggs, one at a time, beating until light and creamy, 2 minutes.
Add the dry ingredients alternately with the greek yogurt and vanilla to the creamed mixture, beat until smooth.
Spread half the batter in the prepared tube/bundt pan, spoon ⅔ of the topping over batter. Cover with remaining batter and top with remaining topping.
Bake for approximately 50-60 minutes or until inserted toothpick comes out clean or a few crumbs attached. After 45-50 minutes if it is not done but is becoming too brown cover with foil and continue to bake. Cool in the pan, then remove to a clean plate. Enjoy!
