Step 1

Before you begin, be sure to prepare the baking tin: Melt a little butter (or DF alternative) and brush the inside of the tins (base and sides). (See NOTES re tin)

Step 2

Base line the tin with good quality non-stick baking paper, cut to size.

Step 3

Pop a teaspoon of extra flour into the tin and tip until the sides are well-dusted with flour.

Step 4

Tip any excess flour from the tin. Set aside.

Step 5

Pre-heat the oven to 180 C/350 F/Gas 4.

Step 6

In a bowl or container, weigh and thoroughly mix together the flour, salt and xanthan gum (if required). Set aside.

Step 7

In a small heat-proof bowl, melt the butter (covered and in a microwave set to medium on 30 second bursts works well). Set aside.

Step 8

Get ready a large heat-proof bowl and a large saucepan with an inch or two of water (over which the bowl sits snugly, but doesn't touch the water).

Step 9

Bring the water to a very low simmer.

Step 10

Weigh the sugar and crack the eggs into the large heat-proof bowl and whisk continually using an electric hand whisk (set over the barely simmering water) for 7 to 10 minutes.

Step 11

Keep whisking until the mixture is pale, has almost tripled in volume and a lasting trail (of a few seconds) can be formed on the surface when the whisk is lifted.

Step 12

Remove from the heat, before sifting the flour across the surface and gently drizzling the melted butter round the edge of the bowl.

Step 13

Quickly and gently fold the flour and butter into the mixture using light and high sweeps with a large spoon (in a circular folding motion), retaining as much air as possible. Fold until the mixture is even, but be careful not to over-mix.

Step 14

Pour the mixture into the prepared baking tin (to a maximum of about two-thirds full) and very gently smooth the surface.

Step 15

Bake for about 20 to 30 minutes until well-risen and light golden. The top should just spring back when pressed and a cake skewer inserted will come out clean. Keep a close eye and check minute by minute at the end to be sure it isn't over-baked.

Step 16

Leave the sponge to cool in the tin for 5 to 10 minutes, before removing and transferring to a wire rack to cool completely. To ensure moisture is retained, cover with a clean tea towel while cooling.

Step 17

Once completely cold, the sponge can be cut and used for trifles. Or if preferred, cut and/or filled as a standard light sponge cake.