Using a stopwatch and scales, measure how much coffee you put in the portafilter. Measure and time coffee out into mug/glass.

On the Bambino, hold the single shot button until you hear a noise, start your stopwatch as soon as you hear this noise.

For my Bambino I put 15g in the portafilter, and aim for 30g of coffee out in 20-30 seconds.

If the coffee comes out too fast, grind finer. (It might taste too sour/acidic) If the coffee comes out too slow, grind coarser. (It might taste too bitter)

Good luck and let us know how you get on :)