First, find a suitable jar - I got these 550ml ones from Asda.
I found the recipe HERE, but I fiddled a little with it to make it fit into the jar.
I used 'cups' as it is an American recipe, you can find measuring cups in a few supermarkets now, mine are quite old now but I find I use them a lot.
I mixed the plain flour (1 + 1/3 cups) with a teaspoon of baking powder and a teaspoon of bicarbonate of soda in a bowl, then I put half of it into the bottom of a jar. I then pressed it down quite firmly with the end of a rolling pin - it is necessary to do this otherwise the rest of the ingredients will not fit into the jar.
Following that was a nice colourful layer of Smarties, at this time of year you can get pink ones in the Christmas Sweetie aisle, I used half a large tube. When I put them in I used a spoon to push as many as I could towards the edge of the jar.
I topped these with a layer (half a bag) of white chocolate chips - again found in the baking aisle. I pushed these to the side too, to give a decent looking layer.
Next came a layer of 1/2 a cup of soft brown sugar, this was quite easy to pack down and sunk into the gaps left by the sweeties :)
Filling up the jar was the final ingredient which was 1/2 a cup of white sugar, when packed this came to the top of the jar perfectly.
Now, just for the remainder of the flour, it's tricky as obviously the jar is full, but there is a little recess in the lid of the jar, so if the flour was piled up like a little pyramid, the lid would push it down to fit the shape - that was the theory and luckily it worked!
But of course........ they needed to be tested :)
So, you empty the ingredients into a bowl (carefully as the flour is likely to spill out when you pop open the jar) and give them a good mix up. Add a beaten egg and 1/2 cup of melted butter and mix very well.
Roll into balls about 1.5" big and place on a baking tray lined with greasproof paper. You WILL need to leave plenty of room inbetween the balls as they spread quite a bit. You should get about 24 balls out of this mixture.
Bake at gas mark 3 for around 15 mins, which should still leave them a little chewy.
Nom them down quickly before the rest of the family finds them :)