A method of producing a permanently joined plate heat exchanger comprising a plurality of metal heat exchanger plates having a solidus temperature above 1000 oC, provided beside each other and forming a plate package with first plate interspaces for a first medium and second plate interspaces for a second medium, wherein the first and second plate interspaces (4,5) are provided in an alternating order in the plate package, wherein each heat exchanger plate comprises a heat transfer area and an edge area comprising bent edges which extend around the heat transfer area, wherein a first surface of the plates forms a convex shape and a second surface of the plates forms a concave shape wherein the heat transfer area comprises a corrugation of elevations and depressions, wherein said corrugation of the plates and the bent edges are provided by pressing the plates characterised in that the method further comprises the following steps: applying a melting depressant composition on at least a part of the first convex surface of a first plate, the melting depressant composition comprising • a melting depressant component that comprises at least 25 wt% phosphorus and silicon for decreasing a melting temperature of the first plate, and • optionally, a binder component for facilitating the applying of the melting depressant composition on the first convex surface, bringing a second concave surface of a second plate into contact with the melting depressant composition on said first convex surface of the first plate by stacking the plates (21, 22) into a plate package, and heating the first and second plates (21, 22) to a temperature above 1000 oC, said first convex surface of the first plate thereby melting such that a surface layer of the first plate melts and, together with the melting depressant component, forms a molten metal layer that is in contact with the second plate at contact points between the first plate and the second plate, and allowing the molten metal layer to solidify, and form a joint at the contact points between the plates in the plate package and such that the bent edges form a tight fit between the bent edges of the plates in the plate package, the joint comprising at least 50 wt% metal that, before the heating was part of any of the first plate and the second plate. applying a melting depressant composition on at least a part of the first convex surface of a first plate, the melting depressant composition comprising • a melting depressant component that comprises at least 25 wt% phosphorus and silicon for decreasing a melting temperature of the first plate, and • optionally, a binder component for facilitating the applying of the melting depressant composition on the first convex surface, • a melting depressant component that comprises at least 25 wt% phosphorus and silicon for decreasing a melting temperature of the first plate, and • optionally, a binder component for facilitating the applying of the melting depressant composition on the first convex surface, bringing a second concave surface of a second plate into contact with the melting depressant composition on said first convex surface of the first plate by stacking the plates (21, 22) into a plate package, and heating the first and second plates (21, 22) to a temperature above 1000 oC, said first convex surface of the first plate thereby melting such that a surface layer of the first plate melts and, together with the melting depressant component, forms a molten metal layer that is in contact with the second plate at contact points between the first plate and the second plate, and allowing the molten metal layer to solidify, and form a joint at the contact points between the plates in the plate package and such that the bent edges form a tight fit between the bent edges of the plates in the plate package, the joint comprising at least 50 wt% metal that, before the heating was part of any of the first plate and the second plate.