Scarlett Johansson has had her turn as an ambassador for major beauty brands, and now the “Black Widow” star is giving them competition with the launch of her own clean skin care line, The Outset. Founded on the concept of beginning with the basics and building an effective, universal routine, the brand is a reflection of Johansson’s own uncomplicated approach to beauty. The Outset, which launched in March and is now available at Sephora, is a curated offering of five products, collectively the result of over five years of development. After learning about the beauty business and experimenting with formulations for several years, Johansson met co-founder Kate Foster, an entrepreneur…