In this paper we characterize the $c$-Boomerang Connectivity Table (BCT), $c\neq 0$ (thus, including the classical $c=1$ case), for all monomial function $x^d$ in terms of characters and Weil sums on the finite field~$\F_{p^n}$. We further simplify these expressions for the Gold functions $x^{p^k+1}$ for all $1\leq k<n$, and $p$ odd. It is the first such attempt for a complete description for the classical BCT and its relative $c$-BCT, for all parameters involved.