- Except lukewarm water, place the rest of dough ingredients in a mixing bowl. Gradually stir in the water to form a smooth dough. Allow the dough to rest for 15 minutes covered with a plastic film. Line 2 baking trays with parchment papers. Place the dough on the work-top and roll it out to a rectangle 60 by 20 cm. Fold the top and bottom of the rectangle into the centre, folding the dough into thirds. Repeat the rolling and folding process twice more without the necessity of resting the dough.
- After the dough has been folded in thirds three times, roll it out until it is about 1/4 cm thick. Use a fork to prick the dough thoroughly. With a pizza wheel, cut the dough into 5 cm squares or cut shapes with desired cookie cutter. Using a spatula, transfer the crackers to the prepared baking trays. Cover and let cookies rest for 15-20 minutes.
- Preheat the oven to 180C/350F. It is ready to bake the cookies when they have risen to 4 mm high. Bake the cookies in the preheated oven for about 18 minutes until firm. When you press them lightly with your finger, almost no imprint will remain. Cool them completely.
- Beat the butter in a bowl until smooth. Add in powdered sugar, vanilla and milk. Beat until combined and smooth. To make sandwich, spread one cracker with the buttercream and top with second cookie, pressing gently.