“if you have just used the milk frother, it still takes a bit of time to rebuild enough pressure to make a new espresso .”

Actually, the machine is cooling down, not rebuilding pressure.

You can force it to cool down quicker by switching from steam mode (press steam or coffee button so that the steam light goes out and the coffee buttons flash) then open the water/steam tap by twisting the knob anticlockwise. steam and then water will flow out of the nozzle until the machine has cooled down (about five seconds). Close the tap when the coffee lights stop flashing and remain on steady, at which point you can immediately make coffee again.