Preheat the oven to 400°F (200°C). Line a baking sheet with a silicone baking mat or parchment paper.
In the bowl of a stand mixer, combine the flour, baking powder, and salt. Add the cold butter and mix until the butter is broken into pea-sized pieces.
Add the chopped walnuts, heavy cream, egg, pure maple syrup, and brown sugar. Mix just until a shaggy dough forms and no dry flour remains. Do not overmix.
Divide the dough into 10 equal portions and place them on the prepared baking sheet, leaving about 2 inches between each scone. Brush the tops with heavy cream.
Bake for 18 to 20 minutes, or until the tops are lightly golden and the scones are baked through.
Transfer the scones to a wire rack and let them cool for 15 minutes.
For the icing:
Whisk together the powdered sugar, pure maple syrup, and heavy cream until smooth. Spoon a dollop of icing into the center of each cooled scone and allow it to spread naturally over the top. Let the icing set for a few minutes before serving.
Notes
Use cold butter straight from the refrigerator for the most tender scones.
Toast the walnuts before adding them to the dough for a deeper, richer flavor. Let them cool completely before mixing them in.
Scoop the dough into evenly sized portions so all of the scones bake at the same rate and finish at the same time.
Store leftover scones in an airtight container at room temperature for up to 2 days or refrigerate for up to 5 days. Freeze for up to 3 months.