Boozehound by Jason Wilson has the best recipe for this tasty classic. Not to mention its a great book!
2 oz gin - I like Barr Hill best
3/4 oz lemon juice
1/4 oz Luxardo Marashino
1/4 oz Creme de Violette
I recommend straining lemon juice first so there is no pulp in drink. Build in shaker, then double strain into chilled coupe. Garnish with quarter size and shape of lemon peel so it looks like the sun in the blue sky!