1preheat oven to 350°. Coat a 9 inch round 2 inch deep cake pan with nonstick spray.
Stir together the 3/4 cup Brown sugar, cream, and a pinch of salt for the caramel topping in a measuring cup. Pour caramel into the prepared pan, spreading to coat bottom of the pan. Sprinkle pecans over caramel.
2Process the 1/2 cup Brown sugar, 1/3 cup flour, 4 tablespoons butter, cinnamon, and 1/4 teaspoons salt for the streusel in a food processor, pulse until mixture is sandy but without clumps. Set streusel aside.
3Whisk the 1 1/2 cups flour, baking powder, baking soda, and 1/2 teaspoon table salt for the cake in a bowl. Set dry ingredients aside.
4Whisk together buttermilk, yogurt, and eggs in a measuring cup with a pouring spout. Set aside.
Using a hand mixer, cream together the one stick butter and three quarter cup sugar in a bowl only until combined. Alternately add flour mixture and buttermilk mixture to the creamed mixture, starting and ending with flour mixture. Blend only and not to incorporate the dry ingredients into the batter.
Spread half of the batter over the caramel in the cake pan, then sprinkle with half of the streusel. Carefully spread remaining batter over streusel in cake pan. Top with the remaining streusel.
5Bake coffee cake until a toothpick inserted in the center comes out clean, 50 to 60 minutes. Cool cake for five minutes on a rack, then run a paring knife around the sides to loosen cake.
Let coffee cake cool slightly before serving.