Catalyzes the synthesis of lactosylceramide (LacCer) via the transfer of galactose from UDP-galactose to glucosylceramide (GlcCer) (PubMed:9593693). LacCer is the starting point in the biosynthesis of all gangliosides (membrane-bound glycosphingolipids) which play pivotal roles in the CNS including neuronal maturation and axonal and myelin formation (By similarity). a beta-D-glucosyl-(1<->1')-N-acylsphing-4-enine + UDP-alpha-D-galactose = a beta-D-Gal-(1->4)-beta-D-Glc-(1<->1)-Cer(d18:1(4E)) + H(+) + UDP Inhibited by EDTA. Optimum pH is 7.2. Protein modification; protein glycosylation. Sphingolipid metabolism. Trans cisternae of Golgi stack. Highest expression in brain with lower levels found in lungs, heart, skeletal muscle and kidney. Lowest expression in testis, liver and spleen. Belongs to the glycosyltransferase 7 family.