Select Steambake on your oven and preheat to 205°
Add the self-raising flour, baking powder, salt and mustard powder into a large bowl and mix together.
Combine the butter and crumble by hand until it looks like sand.
Sprinkle in the cheddar and thyme.
Crack the eggs into an empty jug and pour in the milk.
Add the sour cream and stir well. Then pour over the dry mixture and mix until stiff.
Spread some flour and roll the mixture until 2cm thick. Then cut into shape.
Place on a tray, brush with milk and scatter with cheese.
Pour water in the base of the oven. Steambake for 15 minutes to blast moisture into the food followed by a shot of dry heat for fluffy middles & a lovely, crispy outer-texture.
Serve immediately and enjoy