Preheat the oven to 220°C/425°F (200°C fan) and line a large baking tray with baking paper.
Add the self-raising flour and cold butter to the Thermomix bowl. Mix for 15 sec/speed 5. The mixture will resemble fine breadcrumbs.
Add the caster sugar, salt and milk. Mix for 5 sec/speed 3.5 to just combine. Then knead for 20 sec/dough setting, until the dough just starts to come together.
Turn the dough out onto a lightly floured surface and gently bring it together with your hands. Gently roll it 3-4cm thick (just move the rolling pin over no more than 3-4 times). Cut into rounds with a 5 cm floured cutter, pressing straight down without twisting.
Place the scones on the lined tray, brush tops with a little milk, and bake for 12 minutes, until golden and risen. Bake for a minute or two extra if needed.
Let the scones cool on the tray for a few minutes then transfer to a baking rack to cool completely. The scones can be served warm.
Notes
Storage: Scones are best enjoyed on the day they are made, but can be stored for 1-2 days in an airtight container.To freeze: Let the scones cool completely and transfer them to a resealable bag or airtight container before freezing for up to 1 month. Defrost for 1 hour at room temperature, then warm the defrosted scones in the oven.