Preheat oven to 400°F. Whisk flour, sugar, salt, and baking powder together in a large bowl. Place in freezer while you grate frozen butter.

Grate the frozen butter and place back in freezer while you mix wet ingredients. Whisk 1/2 cup heavy cream, the egg, and vanilla extract together in a small bowl.

Add frozen grated butter to the flour mixture and combine with a pastry cutter, two forks, or your fingers until the mixture comes together in pea-sized crumbs. Toss Toffee Crumbles with flour mixture and add wet mixture. Stir just until incorporated. Do not over-mix.

To make triangle scones: 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. For smaller scones, press dough into two 5-inch discs and cut each into 8 wedges.

To make 10-12 drop scones: Keep mixing dough in the bowl until it comes together. Drop scones, about 1/4 cup of dough each, 3 inches apart on a lined baking sheet.

Brush scones with egg wash and sprinkle with castor sugar if desired. Place scones on a plate or lined baking sheet and refrigerate for at least 15 minutes. Line a large baking sheet with parchment paper. After refrigerating, arrange scones 2-3 inches apart on the prepared baking sheets.

Bake for 18-20 minutes or until golden brown around the edges and lightly browned on top. Larger scones take closer to 25 minutes. Remove from the oven and cool for a few minutes before topping with optional toppings listed in the ingredients.