Strawberry Rhubarb Pie

2 9-inch unbaked pie crusts
1 c sugar
1/2 c flour
1 lb rhubarb (about 3 large stalks)
2 pints of strawberries
2 TBSP butter
1 egg yolk
Sugar for sprinkling on top

Combine sugar, flour, rhubarb and strawberries. Pour into unbaked pie crust. Dot with 2 TBSP of butter cut into small pieces. Top with second pie crust. Cut several slits in the top crust. Brush crust with egg yolk and sprinkle with sugar. Bake at 425 for 15 minutes, reduce temperature to 375 and bake for 45 more minutes.