In a small bowl, whisk together the egg, sour cream, and vanilla. Set the mixture in the fridge.
In a medium-sized mixing bowl, add the flour, baking powder, salt, and sugar. Cube up your cold butter stick and add it into the dry ingredients.
Using a pastry cutter or your fingers, cut the butter into the flour mixture until the butter pieces are quite small (pea-sized pieces.)
Make a well in the center of the ingredients. Add in the sour cream/egg mixture, fresh blueberries, and crushed hazelnuts.
Gently mix the dry ingredients into the wet ingredients. Once you reach a point where it seems hard to continue mixing in the bowl, pour the dough out onto a clean work surface.
Use your hands to lightly knead the scone dough until it comes together as one.
Form the dough into a circle that is 6" in diameter. Place the giant dough circle onto a sheet of parchment paper and on to a plate or tray. Cover the dough lightly with plastic wrap and let it rest in the freezer for at least 30 minutes, up to overnight.
Macerated Blueberries
In a small bowl, toss the blueberries with the sugar and lavender (if using). Mash up the blueberries, then cover the bowl and place it in the fridge until you're ready to make the glaze. You can make this macerated blueberry mixture up to 48 hours in advance.
Once you're ready to bake the scones, preheat the oven to 425°F / 220°C. Line a cookie sheet with parchment paper or a silicone baking mat.
Slice the scones into 8 equally sized triangles. Evenly space them apart on the lined baking sheet.
If desired, you can brush a little bit of heavy cream on top of the scones to encourage the tops to brown. Bake for 15-20 minutes, or until the scones start to turn golden brown on the tops and bottoms.
Blueberry Glaze
Pour the macerated blueberries through a fine mesh sieve into a small mixing bowl. Add in the powdered sugar, and whisk until combined. If the berries didn't make enough juice for the mixture to come together, you can slowly add in your favorite milk or water until you reach your desired glaze consistency.
Once the scones have cooled to room temperature, top them with the glaze. Serve and enjoy!
My favorite way to do this is with my hands because you have more control in breaking up the pieces of butter. Use your fingers (or a pastry cutter) to cut up the butter into smaller chunks and distribute it throughout the flour, until the pieces are pea-sized. If the butter pieces are too large, they will just melt out while baking rather than giving you lift and flaky layers.
Keep the dough & ingredients cold:
I know I'm always saying to have room temperature ingredients, but another reason scones are great is because you *need* cold ingredients. You'll want to keep your ingredients cold to avoid melting the butter. If at any point your dough seems too warm while putting it together, place it in the freezer for 5 minutes and then continue on with the recipe.
Hazelnuts & lavender:
I added hazelnuts to the dough because they pair so nicely with the blueberries and is nice for some added texture in the scones. You can omit the hazelnuts and replace them with your favorite nut, or just leave them out all together. Same with the lavender - adding it into the macerated blueberry mixture gives you just a nice hint of floral notes in the glaze. You could leave it out or even replace it with dried rose petals which would also be delicious!
Use a kitchen scale:
I can’t stress enough the importance of a kitchen scale for accurate baking. While other things can go wrong during the baking process, using a kitchen scale helps your recipe come out closer to how mine did and can be more helpful for troubleshooting if something goes wrong. Here is a cheaper kitchen scale (affiliate link) that was trusty and helpful when I was starting with a scale. If you can’t use a scale – please make sure that you fluff up your flour with a fork, and spoon it into your measuring cup while measuring the flour.