★★★☆☆ — A childless couple adopts an impossible newborn discovered on their isolated Icelandic farm. Much like Ari Aster’s Sweden-set Midsommar, Lamb — the directorial debut of Valdimar Jóhannsson, who co-wrote the screenplay with renowned creative Sjón (The Northman) — pairs its unique nordic vistas with an unsettling tale of grief and…