Grease a deep steamer pan or a cake mould with 2 to 3 tsp of oil.
In a mixing bowl, sift besan/gram flour/chickpea flour.
Add turmeric powder, lemon juice, sugar, and salt.
Add 1 cup water or as per requirement to get a thick but flowing batter consistency (water requirement depends on the quality of flour).
Mix well and add the semolina, if using.
If the batter is too thin, add 1 to 2 tbsp gram flour.
Bring to a boil 2 to 3 cups (or as required) of water in a steamer or a stove-top cook-pot.
Now add the baking soda or fruit salt to the batter.
Stir quickly until evenly mixed into the batter (to prevent uneven levening).
Pour the batter in the greased pan.
Place the pan in a steamer cook-top and cover with the lid.
Let it steam for 15 to 20 minutes in an electric cooker on a medium to high heat.
Once steamed, do the toothpick test check doneness. If the toothpick comes out with uncooked batter on it, then steam a bit more.
When the khaman cools down a bit, then slide in a spatula gently sliding along the edges and invert the pan to slowly drop the khaman dhokla on a plate.