Preheat oven to 350 degrees. Spray a 9-inch round cake pan with nonstick spray.
Stir together brown sugar, cream, and salt for the caramel. Pour into prepared pan and spread to coat the bottom. Sprinkle pecans over the caramel.
Process brown sugar, flour, butter, cinnamon, and salt for the streusel in a food processor. Pulse until small clumps form; set aside.
Whisk buttermilk, yogurt, and eggs together for the cake in a measuring cup with a pour spout. Sift flour, baking powder, soda, and salt onto a paper plate.
Cream butter and sugar with a mixer just until combined. Alternately add dry and wet ingredients, starting and ending with the dry. Blend each addition just until incorporated. Spread half the batter over the caramel, then sprinkle with half the streusel. Carefully spread remaining batter over that and top with remaining streusel.
Bake 50 to 60 minutes, or until a toothpick comes out clean. Cool cake for 5 minutes on a rack, then run a paring knife around the sides to loosen. Invert onto a serving platter while hot, then let cool slightly before slicing. Due to the sticky top, use a sharp, thin-bladed knife to slice the cake.
How to Toast Pecans
Preheat oven to 350 degrees. In a shallow, foil-lined pan large enough to hold pecans in a single layer, toast pecan halves just until light golden and fragrant, about 10 to 13 minutes. Stir occasionally, and watch carefully! (nuts can burn quickly). Remove from oven and set aside to cool until ready to use.