Strawberry-Rhubarb Margarita

This is inspired by a Bobby Flay cocktail recipe; it combines my undying love for anything strawberry-rhubarb with my love for cocktails. To my delight, I had found rhubarb bitters at Binny's and determined that I must devote myself to finding a use for it-- so here is one... I hope to find more.

For the Rhubarb Syrup:
1 lb rhubarb, sliced
1 cup strawberries, halved
1 cup sugar
1 cup water

Bring all the ingredients to a boil and simmer for 3 minutes. Cover and let steep for 1 hour. Strain the mixture through a sieve, pressing against solids and let it cool completely.

For the Cocktail:
1 cup white tequila
1/4 cup fresh lime juice
2 T freshly squeezed orange juice
2 T Cointreau
3/4 to 1 cup rhubarb syrup  (start with less and see if you want it sweeter)
egg whites (one per shaker full)
rhubarb bitters

Combine tequila, lime juice, orange juice, Cointreau and rhubarb syrup in a small pitcher. Fill a large cocktail shaker with ice and pour in the cocktail base (it will use about 1/2 the base). Add one egg white and shake vigorously for about 20 seconds. Pour into martini glasses and add a dash of rhubarb bitters. Garnish with a lime slice and a strawberry.