In a small bowl mix the lukewarm water, yeast and sugar. Let the mixture foam for about 15 minutes.

Combine all the dry ingredients together; flour, semolina, and salt. To the dry mixture, add the melted butter, mustard and the activated yeast.

Knead the dough for a couple of minutes, until you get a smooth soft dough.

Place the dough in a bowl, cover and let it rest for an hour.

Preheat the oven to 180°C. Line a baking tray with parchment paper. Set aside.

If you have a pasta machine you can use it, or else a normal rolling pin can do the job. Divide the dough into about 6 pieces as it's best to work is small batches. Roll the dough to about 2mm thick.

With a narrow glass or a small cookie cutter cut the galletti and place them on the baking tray. With a toothpick or fork, make five holes in the middle of each galletta. This will help the dough not to fill with air and puff up while cooking.

Cook for about 15 minutes, until they get a golden colour. Let them cool. You might need to cook all the dough in several batches as this will depend on your oven and baking trays.

They can be enjoyed immediately or later. If stored in an air tight container these galletti can last for about a week as they'll keep their crunchiness.