As the squash cooks it will release some water. The pan should be hot enough that the butter and this water simmers, but the butter does not burn.
I personally find that young squash tastes somewhat bland compared to older squash. So when I harvest my squash from the garden, I store them for a month or two in a cool cellar before I start to eat them. You may find that this recipe works better in late fall and early winter when your squash (either from your garden or from the store) has had a chance to mature.
This is an extremely easy recipe, except for peeling the squash. Squash is a rather tough fruit when raw (yes, I know it looks and tastes like a vegetable, but technically it is a fruit). I find the easiest approach is to cut the squash into strips about an inch wide (following the ridges in the squash) and then to peel and cut the strips.
Cooked squash should be fairly soft, with just a hint of firmness. Ideally it should have the same firmness as a boiled potato just before the potato has been boiled long enough.
Butternut squashes come in a variety of sizes, often quite large. If you buy one that is too large for this recipe, simply peel and cube as much as you need. Cover the rest with plastic (cling film) and it will keep several days in the fridge, when you can repeat the recipe with the remainder. Alternatively, cook all of it and then warm up the leftovers the next day by briefly frying them in butter.
A good butternut squash, like its name indicates, tastes slightly of butter and of nut. This recipe brings out both tastes.
Squash is native to North America and was unknown in Europe until it was imported from North America. Most recipes call for it to be baked or boiled, but a French friend taught me to fry it in butter and I find this is the best way to cook it.
I can't say that this is a traditional French recipe. However, it is too good to exclude simply because it isn't French, and I'll use the excuse that I learned the recipe in France.
Of all the squashes, my favourite is Butternut Squash. In the UK, this is also know as the "Crown Prince" squash. This recipe is intended for this squash; it may work for other squashes, but I make no promises as the different types of squash vary a lot in taste and texture.