How do I create a UV Coordinate that is bended in a quarter circle

[B_REX]

Dear Shader Gods,

I’m trying to create a UMG Widget, that is bended in a circular shape.
Question is how can I bend a UV coordinate so that it is usable as a retainer texture. So basically I want to manipulate from this:

to this

So that

this becomes

Any idea? It must be something with sine and cosine but it totally exceeds my math