Whisk to combine the flour, brown sugar, baking powder, and salt. Add the butter cubes and work them into the flour, breaking them down into small pieces with your fingertips and coating them in the flour mixture. When no large butter pieces remain, add the buttermilk and vanilla extract. Stir around until the dough is moist and cohesive.
Shape the dough into a square (or circle, if you desire triangles instead), and cut into 9 even pieces. Spread them out on a baking sheet and bake for 15 minutes, until cooked through. Let cool completely.
To make the glaze, whisk together the powdered sugar, maple syrup, and milk. Drizzle over the scones, then sprinkle on the pecans.