Briefly mix 140 g butter and brown sugar with the whisk of the hand mixer. Add flour and knead first with the dough hooks of the hand mixer, then briefly with your hands. Halve the dough and roll out each half between 2 sheets of baking paper approx. 2 mm thin. Place on a flat plate and chill for about 30 minutes
Take a pastry sheet out of the refrigerator, remove baking paper from both sides, but only remove the upper sheet of baking paper. Cut the dough into squares (approx. 3.5 x 3.5 cm) with a pizza cutter. Lift the squares immediately onto 2 baking trays lined with baking paper (dough becomes soft when it gets too warm) and bake them one after the other in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 5-6 minutes. Let the finished biscuits cool down on the baking tray, then pull them off the tray with the baking paper and let them cool down completely. Do the same with the 2nd half of the dough. If necessary, knead dough rests/edges together and roll out again
Sift the icing sugar. Cream 150 g butter, icing sugar and speculoos spice. Put the cream into a piping bag and cut off the tip (piping thickness approx. 0.7 cm Ø). Spray a circle on half of the biscuits, cover with the remaining biscuits and press down lightly. Put the cookies in a cool place for about 30 minutes. Packed in tins, store in a cool place
Waiting time approx. 1 hour