Combine the mashed banana, buttermilk, and vanilla into a medium bowl. Set aside.
Whisk flour, brown sugar sugar, baking powder, baking soda, salt, cinnamon and nutmeg together in a large bowl.
Add the cold, cubed butter to the flour mixture and combine with a pastry cutter, two forks, or your fingers (my preference) until the mixture comes together in pea-sized crumbs.
Add the wet ingredients to the dry, followed by 1/3 cup of pecans and mix until everything is just moistened. You may have some straggly bits that aren't completely mixed in. That's ok. Don't overwork the dough.
Scoop the dough onto the counter and, with floured hands, work dough into a flat ball shape. The dough should be sticky. If it seems too dry, and won't stick together well, add 1-2 more tablespoons buttermilk.
Press and form the dough into an 6-inch disc and, with a sharp knife or bench scraper cut into 6 equal wedges.
Place the scones onto a baking sheet lined with parchment paper. Chill in the refrigerator for 30 minutes.
While the scones are chilling, heat the oven to 400F.
Brush the tops of the scones with heavy cream. Sprinkle the tops with turbinado sugar.
Bake for 20-23 minutes or until golden brown around the edges and lightly browned on top.
Remove the scones from the oven and let them cool for 10 minutes.
While cooling, prepare the glaze. Whisk together the espresso powder, espresso, vanilla, and confectioner's sugar until combined.
Drizzle the scones with the glaze and sprinkle the remaining 1 tablespoon of pecans over the scones. Serve warm.