Preheat the oven to 350°F. Line a large, heavy-duty metal baking sheet with parchment paper.

Place the rolled oats and chopped hazelnuts into the bowl of a food processor. Pulse several times until the nuts are finely chopped and unified with the oats.

Add the pastry flour, cane sugar, baking powder, and kosher salt into the bowl. Pulse briefly to distribute the leavening agents. (The massive ratio of 2 tablespoons of baking powder forces a rapid, towering rise in the oven).

Drop the deeply chilled butter cubes directly over the dry ingredients. Pulse the machine repeatedly until the butter is cut into the flour, creating coarse, pea-sized crumbs. Do not overprocess; preserving distinct, cold lipid pockets is critical for a flaky crust.

In a small bowl or glass measuring cup, vigorously whisk together the heavy whipping cream and the egg.

With the food processor running, slowly stream the liquid mixture through the feed tube just until the dough rapidly clumps together around the blade. Stop immediately to prevent the gluten from toughening.

Turn the sticky, shaggy dough out onto a generously floured wooden or marble board.

Use floured hands to gently pat the dough into an 8x9-inch rectangle, about ¾-inch thick. Do not knead.

Using a sharp chef's knife, cut the rectangle evenly into 6 squares. Cut each square diagonally in half to form 12 uniform triangles.

Use a pastry spatula to transfer the triangles onto the prepared baking sheet, leaving 2 inches of space between each.

Bake in the preheated 350°F oven until the scones puff significantly and the edges just begin to turn golden brown, about 20 to 25 minutes. Cool entirely on the baking sheet.

While the scones cool, vigorously whisk together the confectioners’ sugar, whole milk, melted butter, pure maple extract, and brewed coffee in a medium bowl.

The glaze should be thick, opaque, and glossy, but fluid enough to pour. Drizzle heavily over the cooled scones and allow the icing to set into a firm crust before serving.