2 c. toasted pecans, coarsely chopped
2/3 c. packed light brown sugar
2 tsp. ground cinnamon
2 tsp. vanilla extract
12 T. cold unsalted butter, cut into small pieces
2 3/4 c. flour
3 T. sugar
1 T. baking powder
1/4 tsp. baking soda
1 3/4 c. buttermilk
Preheat oven to 350 degrees. Line a 9″ x 13″ baking pan with foil, letting it overhang on the sides: coat with cooking spray.
Spread the pecans in the prepared pan. Sprinkle the brown sugar, cinnamon and a pinch of salt over the pecans. Drizzle the vanilla over the top. Evenly distribute 5 T. of butter pieces over the nut mixture.
Whisk the flour, sugar, baking powder, baking soda and 1/2 tsp. salt together in a large bowl. Work the remaining 7 T. of butter into the flour mixture using a pastry blender until it is pea-sized. Make a well in the center of the mixture. Pour in the buttermilk and stir just until combined. Cover the nut mixture with dollops of the dough.
Bake the coffee cake until barely starting to brown on the top, about 35 minutes. Invert a serving platter or cutting board on top of the hot cake; holding both, carefully turn them over and remove the baking pan. Let cool for 20 minutes. Serve warm.