Given two polynomials ( ), ( ) of degree , we give a combinatorial formula for the nite free cumulants of ( )⊠ ( ). We show that this formula admits a topological expansion in terms of non-crossing multi-annular permutations on surfaces of di erent genera.This topological expansion, on the one hand, deepens the connection between the theories of nite free probability and free probability, and in particular proves that ⊠ converges to ⊠ as goes to in nity. On the other hand, borrowing tools from the theory of second order freeness, we use our expansion to study the in nitesimal distribution of certain families of polynomials which include Hermite and Laguerre, and draw some connections with the theory of in nitesimal distributions for real random matrices.Finally, building o our results we give a new short and conceptual proof of a recent result [Ste20, HK20] that connects root distributions of polynomial derivatives with free fractional convolution powers. * O.A. gratefully acknowledges nancial support by the grants Conacyt A1-S-9764 and SFB TRR 195.