It makes about 18 biscuits.
175g caster sugar
175g plain flour
125g plain flour
Line a baking sheet with some parchment paper.
Preheat oven 180C/gas 4
Beat the butter and sugar together using a mixer till nice and fluffy.
Beat in the egg then add the flours, a bit at a time.
Leave the dough for about an hour to rest.
Take out tbspns of the mixture, roll into a ball then flatten on the baking sheet. Press your thumb in the top to make a hole. Fill the hole with Nutella.
Make sure you space the biscuits out on the baking sheet, because they spread.
Bake for about 12 mins.
Cool on a wire rack.
I can think of a few variations I must try - adding cocoa to make chocolate thumbs, or coffee essence, lemon juice etc. It's a good basic biscuit recipe.