Roll your rolling pin over your crust gently rolling the crust onto the rolling pan so that you can pick it up and gently roll it back out over your pie pan. Once the bottom crust is in, pour out your rhubarb mixture and spread out evenly in your pie plate. Top with about 2 Tablespoons of butter that has been cut into dabs to place all over the top of the pie filling. Then roll your dough over your rolling pin and proceed to roll it back out over the top of the pie.