In a large bowl, whisk together the flour, brown sugar, baking powder, salt and cinnamon until well combined. Work the butter into the flour mixture with your fingertips until pea-sized pieces are formed. Stir in the chopped pecans.
In a small bowl, whisk together the heavy cream, sour cream and vanilla until smooth and well blended. Stir this mixture into the dry ingredients, just until a shaggy dough is formed. Turn the dough out onto a lightly floured surface. Press the dough together and fold it over onto itself a couple of times. Do not overwork the dough. Form the dough into a 6 ½-inch diameter round. Cover and chill in the refrigerator for 30 minutes.
Line a large baking sheet with parchment paper. Cut the dough round into 6 wedges. (For smaller scones, cut the dough into 8 wedges. The baking time for smaller scones will be shorter.) Place the wedges onto the baking sheet about 2 inches apart. Chill the scones in the refrigerator for 15-20 minutes. Top each scone evenly with the pecan topping mixture, about 1 tablespoon each. Spread the topping to within ¼-inch of the edges.
Meanwhile, preheat the oven to 375ºF (190ºC). Bake the scones until the edges are golden brown and the topping is bubbly, about 19-23 minutes. Transfer the scones to a cooling rack.