I recently moved to the US from Sweden, and one thing I sorely miss is idealmjöl. It is a very fine flour that is primarily used to thicken sauces. It has the property that you can just sprinkle it over your sauce and it will dissolve and thicken it (with a little bit of whisking), without making the sauce lumpy. I haven't seen anything obvious in my grocery store that will do the same thing. Is there anything similar here in the States?
The closest thing you are likely to find is a product called Wondra flour. Like idealmjöl, it is a pre-gelated wheat flour, but unlike idealmjöl it also includes some malted barley flour.
One post on this forum implies they may be interchangeable.
You can use pure starch for that, you don't need a flour. If you are careful with the sprinkling, it will work too. But the easiest way is to dissolve a bit of starch with a bit of water in a teacup, and pour into the sauce. No clumping, and it thickens beautifully.
The sauce needs to come to a boil for the starch to work, I don't know if this is needed for your idealmjöl too.