Chai Spice Coffee Cake

Cake:
2 1/2 c. all purpose flour
1 1/2 c. firmly packed brown sugar
1/2 c. sugar
1/2 tsp. salt
1 tsp. cinnamon
1 1/2 sticks butter, softened
1 c. chopped walnuts
1 tsp. baking soda
1 egg
1/2 c. plain greek yogurt
1/2 c. Hellmann's mayonnaise

Topping:
1/4 c. nut mixture
2 Tbsp. sugar
1/2 c. chopped walnuts
1 tsp. cinnamon
1 tsp. chai spice blend

Preheat oven to 350 degrees. Butter and flour 13X9 baking pan.

Combine the flour, brown sugar, 1/2 c. sugar, salt, and 1 tsp. cinnamon in mixing bowl. Blend together with the mixer on low. Add butter and mix until mixture is slightly crumbly. Remove 1 1/2 c. of crumb mixture and add 1 c. walnuts making a nut-crumb mixture. Mix and press 1 1/4 c. of this mixture into 9X13.

Take 1/4 c. of the nut-crumb mixture and make topping. Add 2 tbsp. sugar, 1/2 c. walnuts, 1 tsp. cinnamon, and 1 tsp. chai spice blend. Set aside.

To the remaining crumb mixture in the mixing bowl add baking soda, egg, yogurt and mayonnaise. Mix at medium speed for half a minute until it is a batter. Pour this batter over the crumb mixture in the 9X13. Spread with large spatula to sides making large strokes continually from the middle of the batter to the edges being careful not to upset the crumb mixture on the bottom of the pan. Sprinkle with the reserved topping and bake for 40 minutes. Serve warm or room temperature.