In a bowl, dissolve the yeast in the lukewarm water. Let sit in the counter for 5-10 minutes or until you get a foamy mixture.

To this mixture, add the flour, salt and the melted butter. Mix it well in the bowl to incorporate.

Transfer the dough to a floured surface, and knead it well until the dough is smooth. Alternatively, you can use a stand mixer with the hook attachment for this process.

Spread a little bit of butter in the bowl to prevent the dough from sticking and move the dough there. Cover with cling film and leave it to rise in a warm place for about 30 minutes or until it doubles in size.

In the meanwhile, make a square of butter between two sheets of parchment paper. It's easier to make it by beating small cubes of butter with a rolling pin until it gets thinner (about 1 cm thick). Trim the sides to make a square of about 10x10 cm. Refrigerate until ready to use.

Once risen, roll the dough in a floured surface until you get a square that is bigger than your butter square (about 15-17 cm large).

Place the butter in the middle of the dough, and close the dough on top of it like an envelope.

Carefully roll the dough with the butter inside until you get a rectangle of about 50x25 cm (I use the rolling pin as a guide).

Fold the dough in three thirds, one on top of the other and put it in the fridge overnight.

Now, sprinkle sugar over your working surface and turn the dough with the "open" side (where you can see the folds) facing you.

Roll the dough lengthwise as a rectangle of the same size again. Sprinkle sugar generously on top and fold again in thirds.

The dough is ready to use, so now roll it to all directions until you get a square of about 0.5 cm (¼ inch) thickness all over, making sure the working surface is all coated in sugar.

Grease and sprinkle a thin coat of sugar on each cavity of a muffin pan. Set aside.

Sprinkle sugar over the top again, and cut the dough into 12 even squares.

For each square, press the edges into the center and place them on the muffin pan cavities.

Let the dough rise for about 30 minutes at room temperature and bake at 190°C/375°F for about 40-45 minutes or until caramelized and browned all over.

Once baked, wait a couple of minutes and remove it from the pan while it's still hot -- otherwise it will stick to the pan and you won't be able to remove them.