Preheat oven to 400F. Mix together walnuts, brown sugar and cinnamon in a small bowl.
Bring maple syrup and 4 tablespoons butter to boil in a small saucepan over medium heat. Boil 30 seconds, then scrape into a 10-inch cast iron or heavy skillet of pan. Top with one-third of walnut mixture.
Combine flour, baking powder and salt in large bowl. Add 7 tablespoons butter and mix until the mixture resembles small peas. Add milk; stir gently, just until the mixture comes together.
Melt remaining 1 tablespoon butter in a small saucepan.
Turn dough onto a lightly floured surface and knead gently 5 or 6 times. Roll into a 9 x 12-inch rectangle. Brush with melted butter.
Cover dough evenly with remaining walnut mixture, patting gently. Roll up dough to for a 12-inch log, pinching seam to seal. Cut into 12 (1-inch) slices and place in pan. Bake 25 minutes. Remove from oven and immediately invert onto a large plate (do this quickly, but carefully—the syrup is very hot). Scrape any syrup from pan and spread over buns. Serve warm or hot.