We have accumulated enough measuring spoons (typically from garage sales) to dedicate them for specific purposes, which means keeping them from wandering away:
The design is simple enough:
The slot is a rounded rectangle about 2 mm larger than the spoon handle in both directions, inside a rounded rectangle large enough to put the handle just clear of the jar. The curved side comes from outsetting the jar lid OD by a millimeter (for the double-sided foam tape), then subtracting that circle from the holder.
So, yeah, they’re custom-made for the spoon and jar in hand.
They come from a sheet of 1/4 inch = 6.3 mm Vintage Acrylic. The holder on the smaller jar is two stuck together with super-whoopie low-surface-energy tape before being stuck to the lid. I’m trying the tape on some non-critical projects to see how it behaves: so far, so good.
The Smell of Molten Projects in the Morning 
Good idea and use of your warped acrylic. Parts that small will never show the curvature. Now to make 5K more and open a etsy store ;-)
Why not put them on the jar rather than the lid?
Turns out the first spoon was slightly taller than the jar, so the holder had to go on the lid and I got stuck in that rut.
Just checked: the second jar is just tall enough. Done!
Thanks for the hint …