Mix flour, yeast, sugar and salt in a bowl. Rub in the butter.
Add the egg and warm milk and mix to form a soft dough.
Knead for 8–10 minutes until smooth.
Place in an oiled bowl, cover and leave to rise for 1 hour until doubled.
Divide into 9-10 pieces and roll into smooth balls. Flatten slightly.
Place on a lined tray and leave to prove for 30–40 minutes.
Brush with egg wash if using.
Bake at 200C (180C fan) for 18–20 minutes until golden.
Cool slightly before splitting.
For clotted cream: Heat oven to 90C (80C fan). Pour cream into a wide shallow dish about 3–4cm deep.
Bake uncovered overnight (10–12 hours) until a thick golden crust forms.
Cool completely, then refrigerate for at least 8 hours.
Lift off the thick clotted cream and gently stir. Store in the fridge.
For jam: Add strawberries, rhubarb, sugar and lemon juice to a pan.
Heat gently until the sugar dissolves. Stir in the pectin.
Bring to a strong boil for 8–10 minutes until thickened.
Test on a cold plate. If it wrinkles, it's ready. Pour into sterilised jars.
To serve: Split the Cornish buns while still slightly warm. Add butter, jam and a generous spoon of clotted cream.
