Preheat oven to 350°; coat a 9 pan with nonstick spray.
Stir together brown sugar, cream, and pinch of 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 1/4 teaspoons salt for the streusel in a food processor. Pulse until small clumps form; set aside. If you don't have a food processor, do it by hand.
Whisk buttermilk, yogurt, and eggs together.
Sift flour, baking powder, soda, and 1/2 teaspoons salt together.
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 40-45 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.
The top is a little sticky, so use a sharp thin bladed knife to cut.