In a medium bowl, dissolve yeast with a quarter cup of lukewarm water and sugar and stir for a few seconds until bubbles form.
Add semolina flour, flour, salt, and a cup and a half of lukewarm water to the bowl, and mix well until you get a uniform and smooth mixture similar to pancake batter.
Cover the bowl with a towel and set aside for an hour until large bubbles form in the batter. In winter, the process can last an hour and a quarter to an hour and a half. Do not mix the batter.
Lightly spray a non-stick pan with oil or grease it with an oiled paper towel. Use a pan about 26 cm (10 inches), while the bottom is about 20-21 cm (8 inches).
Pour about ½ cup of the batter. Tilt the pan gently to the sides to allow the batter to spread on the bottom. If it doesn't cover the bottom, add 1-2 tablespoons.
Place the pan on the stove while it's still turned off. Turn on medium-high heat, and cook for 3 minutes until the top is dry when you touch it. Large holes will appear at this point, which means you are on the track.
Lower the heat, cover, and cook for another two minutes. Remove the Lachuch from the pan and let it cool on a clean towel* see a note at the bottom.
Turn the pan over and run it under tap water for two to four seconds to cool it. Dry the pan with a kitchen towel.
Remember: don't mix the batter - it will "break" the bubbles, which are essential for the typical holes and the spongy texture.
It is important to cool the pan after each Lachuch - some even work with two to four pans, one after the other, to allow them to cool.
The Lachuch can be kept in the refrigerator for up to a week in a plastic wrap or bag. After you take it out of the fridge, heat it in the microwave for about 10 seconds.