These are very easy and go well with posset or creamy desserts (they are also less heavy than shortbread).
You need:
125 gr butter
125 gr glass sugar
125 gr flour
1 egg
2 tablespoons milk
You can add half a teaspoon of vanilla essence if you wish.
Melt the butter. Add the sugar, flour, egg and milk in this order. Mix it all well ( you can do this easily with a wooden spoon). Cover a baking tray with baking parchment or a silicon mat. Make 7-8 cm long lines with the mixture (you can either use a piping bag or a teaspoon). Bake in a 180 degrees preheated oven for 10 minutes. As soon as you see that the edges get golden take them off the oven. Let them cool on a rack.
It is very easy for the children to help with these, except that they are not dexterous with the pipping bag.