A method of manufacturing a composite part (70) for a wind turbine blade (10), the method comprising the steps of providing a mould (50) comprising a mould depression (51) with a floor surface (53) and an adjacent receiving section (54), and a mould inlay (60) having an insertion section (61) and a first side (63); arranging the insertion section (61) in the receiving section (54) of the mould depression (51) so that a junction of the first side (63) and the floor surface (53) forms a first mould edge (66); arranging a fibre material (74) on a moulding surface (52) adjacent to the junction and the first side (63); infusing the fibre material (74) with a resin (75) and curing the infused fibre material (74) to manufacture the composite part (70) having a first part edge (73) being formed by the junction, wherein the material of the first side (63) is chemically inert with the resin (75).