Preheat oven to 400°F. Line 2 half sheet baking pans with a Silpat or parchment paper. Set aside.
In a medium bowl, whisk the cream, brown sugar, maple syrup, and egg together until no lumps remain. Set aside. In a large bowl, whisk the flour, baking powder, and salt together.
Using a box grater, grate the frozen butter and add it into the flour mixture, a little at a time and lightly tossing it and flour together as you go. Once all the butter has been added, cut it into the flour with a pastry cutter, two forks, or your fingers until the mixture resembles coarse meal.
Pour the wet ingredients into the flour mixture, add in the walnuts, and stir the mixture together until everything appears moistened. Try your best to not overwork the dough at any point...you should still see little pieces of butter in the dough.
Using a large cookie scoop, portion out 1/4-cup mounds of the dough onto prepared baking sheet at least 3-inches apart (you might need to use a spoon to help get the dough out of the scoop...dough will be sticky and a little wet).
Brush scones with cream, then sprinkle with coarse sugar if desired.
Bake scones for 20-25 minutes, rotating pans after 10 minutes, until lightly golden and cooked through. Remove from the oven and cool on pans as you make the glaze.
For glaze, melt the butter and maple syrup together In a small saucepan over low heat, whisking occasionally. Once the butter has melted, remove from heat and whisk in the sifted powdered sugar. Drizzle over still warm scones and let glaze set about 5 minutes (if you can wait that long!). Serve & enjoy!