Preheat your oven to 170 C/ 325 F/Gas Mark 3 standard or (150 C/300 F fan )
Using a very large mixing bowl or a free standing mixer put your 400 grams (14 oz) butter/baking spread in with your 400 grams (14 oz) sugar.
Beat with an electric whisk or mixer for 4 minutes. You can use a wooden spoon too. The mixture will pale and thicken a little.
Now add the 8 eggs, 400 grams (14 0z) flour, salt and 3 tbsp milk.
Beat again for about 4 minutes until it's a soft dropping consistency that falls off a spoon easily.
Line a 22 cm by 32 cm metal baking tray with baking paper (not greaseproof otherwise it will stick).
Fill with your batter and gently level off with a spatula or back of a spoon.
Bake for about an hour and ten minutes at 170 C/ 325 F/Gas Mark 3 standard (150 C fan/300 F). If the top starts to catch towards the end of baking time then turn down to 150 C/300 F standard (130 C fan)/ Gas Mark 2 but check after an hour by inserting a skewer or cocktail spoon to see if it comes out clean. It's important not to overbake as no one likes a dry cake.
Allow to cool for five minutes or so in the tin before using the baking paper to gently remove from your tin. Carefully remove your baking paper and allow to cool on a wire rack.
Mix the buttercream icing ingredients together. I like to use a food processor as it stops the icing sugar from going everywhere. But using a electric whisk or wooden spoon works too.
Now if you are confident to cut this cake in half freehand then do so but I like to use a ruler and go round the whole cake marking halfway up so I can easily use a large knife to slice that baby in two.
Spread with your favourite jam and top with blobs of buttercream smoothing flat with a flat spatula. Go right to the edges.
Top with the sponge and dust with icing sugar.
Cut into squares. I go 6 along and 4 across to get 24 cute pieces. Or 4 along and 3 across to get 12.
Pour yourself a cup of tea.