'let...in' expression in Scala

In OCaml, the let...in expression allows you to created a named local variable in an expression rather than a statement. (Yes I know that everything is technically an expression, but Unit return values are fairly useless.) Here's a quick example in OCaml:

let square_the_sum a b = (* function definition *)
    let sum = a + b in (* declare a named local called sum *)
        sum * sum (* return the value of this expression *)

Here's what I would want the equivalent Scala to look like:

def squareTheSum(a: Int, b: Int): Int =
    let sum: Int = a + b in
        sum * sum

Is there anything in Scala that I can use to achieve this?