Hi Nadine - I had a good chuckle from your request because I've been there on wondering just what a "dash" meant. The worst part of something like a Cosmopolitan is that many places adapt the original (or "standard") recipe a bit - makes it hard to figure out how to duplicate the exact taste you favor. But, here are the basic proportions of a standard Cosmopolitan - play with the proportions until you get the taste you love:

For one drink:

1 1/4 ounces Absolut Citron vodka (about 2 1/2 tablespoons)
1/4 ounce Rose's lime juice (about 3/4 tablespoon)
1/4 ounce triple sec or Cointreau (about 3/4 tablespoon)
1/4 cup cranberry juice
1 cup ice cubes
Garnish: lime twist

In a cocktail shaker combine all ingredients. Shake well and strain into a Martini glass. Garnish with lime.