Preheat oven to 475 degrees. Lightly grease a 9” round cake pan (at least 2” deep) or Bundt pan. Heat maple syrup, butter and brown sugar until just melted in a saucepan; remove from heat. Add flour and stir well. Stir in chopped bacon and nuts. Pour mixture into prepared pan, spreading evenly across bottom.
For biscuits: in a large bowl, combine flour, baking powder, soda and salt. Using a pastry cutter or fingertips, quickly work cold butter into flour mixture until crumbly and pieces are pea-sized or smaller. Make a well in center of flour/butter mixture and add buttermilk; mix by hand or with a spoon until dough comes together in a rough, sticky ball. This may require an additional 1-2 T flour. Dough should be wet but still able to hold its shape when handled and formed into balls.
Combine cinnamon and sugar. Drop heaping tablespoonfuls of biscuit dough into melted butter and gently coat; move buttered dough balls into cinnamon-sugar and lightly toss to coat; work in small quantities and do not handle dough roughly or biscuits will not be light and flakey.
Place coated dough balls on top of maple-bacon syrup, covering pan completely in a tight, single layer for best results and even cooking. Bake 15 min. Do not open oven door. Turn oven off and allow biscuits to bake in residual heat an additional 10-12 min, until puffed and golden brown on top.
Remove from oven and place a large plate/serving platter upside down over biscuits. Holding plate in place, quickly invert hot biscuits in one motion onto plate. Do not allow biscuits to cool in pan or syrup will rapidly set up hard. Serve immediately with coffee or tea.