Get everything cold. And I mean cold. If you have time, put your dry ingredients in the freezer for 20 minutes before mixing. Your butter must be fridge-cold and firm to the touch.Add all the dry ingredients into a bowl, plus half the grated Cheddar cheese.Cut the butter into 2cm cubes. Using the paddle attachment or your fingertips, work the cold butter into the dry ingredients, along with the chopped gherkins for about 30 seconds. Only go so far that the butter is in irregular-sized pieces. You need some larger bits of butter to get the layers later.Now, add the buttermilk in a steady stream and mix until it is looking just hydrated – there can still be dry bits.Tip onto a clean surface and push together, scraping all the dry bits into the middle.Roll to approximately 40cm long, sprinkle over half of the leftover cheese and perform a single fold – that’s when you bring the top down two-thirds and then the bottom over the middle third, like a business letter!Turn 90 degrees and roll to 40cm long, then sprinkle over the rest of the cheese and perform another single fold. Use a knife or a bench scraper to cut the folded edge – this will give you the best layers possible.Pat the dough into a rectangle around 2.5–3cm high. Trim the edges (you can bake these as snack scraps!) and pat down slightly to get the dough back into proportion. Cut into six large squares. Place on a baking tray lined with baking paper and put into the freezer for 15 minutes or the fridge for 45 minutes.Preheat the oven to 220°C/200°C fan.Gently brush the tops of the scones with egg wash, if desired. Bake for 12–15 minutes (watch the colour), then turn the oven down to 190°C/170°C fan and continue cooking for 5–10 minutes until the scones are golden and well baked. Transfer to a cooling rack to cool, then serve warm.