Pre-heat the oven to 175°C (350°F) and grease a muffin tin.
Beat the butter, vanilla sugar (or essence), and sugar together until nice and fluffy. Add the flour and mix until a dough forms. Place the dough in the fridge for around 15 minutes to firm up a little.
Divide into six. Roll a little to get a rough ball shape, then flatten each one down inside the muffin tin holes, gently pushing so that the dough moves up the sides creating a large crater.
Bake for around 10 minutes, just until the edges begin to brown (they will look pale and be very soft to the touch).
Remove from the oven. The holes will have closed up a little when baking, so just use the back of a small spoon (or similar) to press the cookie down and re-create the large craters. Leave to cool completely.
Remove from the muffin tin (they should just pop out fairly easily) and fill with your blackberry icing, or whatever else you fancy, Enjoy!