Instructions

Whisk flour, baking powder, cinnamon, and salt together in a large bowl. Grate the frozen butter using a box grater. Add it to the flour mixture and combine with a pastry cutter, two forks, or your fingers until the mixture comes together in pea-sized crumbs. See video above for a closer look at the texture. Place in the refrigerator or freezer as you mix the wet ingredients together.
Whisk 1/2 cup heavy cream, brown sugar, the egg, and vanilla extract together in a small bowl. Drizzle over the flour mixture, add the chocolate chips and cornflake crunch, then mix together until everything appears moistened.
Pour onto the counter and, with floured hands, work dough into a ball as best you can. Dough will be sticky. If it’s too sticky, add a little more flour. If it seems too dry, add 1-2 more Tablespoons heavy cream. Press into an 8-inch disc and, with a sharp knife or bench scraper, cut into 8 wedges.
Brush scones with remaining heavy cream.
Place scones on a plate or lined baking sheet (if your fridge has space!) and refrigerate for at least 15 minutes.
Meanwhile, preheat oven to 400°F (204°C).
Line a large baking sheet with parchment paper or silicone baking mat. After refrigerating, arrange scones 2-3 inches apart on the prepared baking sheet(s).
Bake for 22-25 minutes or until golden brown around the edges and lightly browned on top. Remove from the oven and cool for a few minutes. 
Prepare the glaze by whisking together all of the ingredients until homogenous. Pour over scones and let harden.
Leftover scones keep well at room temperature for 2 days or in the refrigerator for 5 days.