Combine sugar, water, cardamoms, and lemon juice in a saucepan. Bring to a boil over medium heat, and cook until the sugar dissolves. Remove from heat and set aside.
Prepare the dough by mixing dry milk powder, all-purpose flour, baking soda, and melted butter. Slowly drizzle in the milk in small additions, gently kneading with the tips of your fingers to form a cohesive dough. The dough shouldn’t be too hard nor too soft. To check if the texture is right, roll a small amount of dough between your palms for 30 seconds. The ball should be smooth and firm. If you notice cracks in the ball, knead more milk into the dough (a teaspoon at a time).
Only regular full-fat dry milk powder will work for this recipe (brands such as Nido and Carnation are excellent choices); avoid brands such as Everyday and Coffeemate, as they are formulated differently. Also, when purchasing a brand such as Nido, please make sure you are getting the basic milk powder, and not the infant/toddler formula. Lasty, it is essential to use a full-fat (whole milk) powder; nonfat will not work.
If the dough seems too dry out while rolling into balls, add a splash of milk to the dough and gently knead it.
Gulab Jamun can be served warm, cold, or at room temperature.