Extracting an expression matching a pattern from a large expression

Question

I have a Mathematica expression that contains a single square root, schematically

expr = a / (b + Sqrt[c]);

where a,b

Answer 1

Theoretically, this should work correctly:

extractSqrt = Cases[ToBoxes@#, SqrtBox@x_ :> ToExpression@x, Infinity] &;

extractSqrt[expr]