Trevor Bange suggested it was like a muscle that needed exercising. That means taking the time to fly circuits when the crosswind was within but at the upper limit of your comfort level for the aircraft at hand. At the end, your comfort level will have shifted higher (or lower depending on the scare factor).
The idea is to be good and confident (at the same time) with the combination of location, conditions and aircraft. It only makes sense if the conditions are right for training. Some days the risks are just a little too high - gusty and increasing crosswinds are not my favourite. I have given it a rest after only three crosswind landings because the wind was clearly increasing and turning. But three was better than zero or a ground/runway loss of control.
Answer: More is better. Lots is almost enough.
I remember one dual flight where we could have done crosswind landings but elected to land across the grass strip not because it was super windy but because my landings weren't that great and it was entirely possible to land into the wind at that location and take off over an empty field on the other side.
A bit later, well after my solo flight, I was faced with a pretty stiff crosswind so rather than land parallel to the runway I used the lack of obstacles to fly a track 30 degrees across the centreline from right to left. I lined up to fly between the runway gables. I landed right on the centreline and rolled between the gables on to the taxi way which was parallel to the runway. By then I was slow enough to turn back parallel, up the taxi way.
If the wind was coming from the other way I might have had a go at landing on the taxi way and rolling on to the runway. Or I might have stayed home. The point being, I thought all this through before I tried it out and there were plenty of days I decided it wasn't worth the risk to practise crosswind landings. Other days (overcast, passing showers) it was pretty much the only flying I was going to get.