Set oven to 350 deg F. Shelf across the centre.
Get a baking tin that is about 9 ins square, and about 2 deep, or similar: a chicken-size roasting tin works well: line it with non-stick baking parchment.
Now mix up as follows;-
Sift together into a large bowl,
1 and 1/2 cups plain flour (5 - 6 oz)
3 tablespoons cocoa powder (scant oz)
1 teasp bread soda (bicarbonate of soda)
half teasp salt
1 cup caster sugar (6 oz)
Stir them together and then make 3 holes in the surface; a small, a medium and a large.
Into the holes, pour, respectively, 1 teasp vanilla essence; 1 tablespoon vinegar; 5 tablespoons of cooking oil.
Over the top of everything pour 1 cup of cold water (8 fl oz).
Stir everything briskly together with wooden spoon until no flour is visible but don't prolong the mixing.
Pour into prepared tin, bake in prepared oven for half an hour, then check.
Let cool in tin, it is fragile.
When cold, sift a little icing sugar over to decorate (confectioner's sugar, I think)
Needs no garnish.
Raspberries are good with it though, for a dessert.
