Bake both pie crusts blind for 8 minutes. Remove from oven to rack. Decrease oven temperature to 375 degrees.
In large saucepan on low melt butter and chocolate, stirring occasionally. In medium bowl, combine sugar and flour with wire whisk. In another bowl, whisk together eggs, vanilla and evaporated milk. Add a couple of tablespoonfuls of the melted chocolate mixture to the egg mixture and stir.
Add both sugar and egg mixtures to pan of melted chocolate. Stir to combine. Increase heat to medium and stir constantly for 10 minutes.
Evenly divide filling between the 2 pie pans. Bake for 30 minutes.