How to make it

1. Preheat the oven to 350°F. Line a baking sheet with parchment paper and set aside.
2. Stir the oat flour, all-purpose flour, sugar, baking powder and salt together in a mixing bowl. 
3. Use a box grater to grate in the cold butter. Use a pastry blender or two knives to work in the butter a little further, then switch to your hands, rubbing the mixture between your palms to flatten out the butter pieces. Stop when you no longer feel round pieces of butter.
4. Whisk the milk, whole egg, egg yolk and vanilla together and add all at once to the flour. Stir until the liquid isn’t running but the dough still has not come together. Tip everything out onto a work surface, add the chocolate chips and bring the dough together by flattening and folding the dough over itself, scooping up the rogue crumbs and flour and working them in as you flatten and fold. 
5. Flatten and shape the dough into a disc out the dough with your hands to ½ inch thick and about 8 inches across. Cut the disc into 8 wedges. Place on the baking tray, leaving 2 inches (5 cm) between each scone. Dip your fingers in the egg white or and pat the tops. 
6. Bake the scones for about 20 minutes, until golden brown on the top and bottom. Let the scones cool on the try on a rack.
7. For the drizzle, melt the chocolate chips and butter in a small saucepan over medium low heat while stirring, or in the microwave.  Use a fork or piping bag to drizzle the chocolate over the scones and let the chocolate set an hour before enjoying.
8. The scones are best enjoyed the day they are baked, but can be stored in an airtight container on the counter for up to 2 days.