Preheat oven to 350 degrees F. In a food processor combine crushed crackers, cashews, and granulated sugar. Cover and pulse with several on/off turns to form fine crumbs. Add the melted butter; cover and pulse with several on/off turns to combine. Press mixture onto the bottom and up the sides of a 9-inch pie plate. Bake for 8 to 10 minutes or until fragrant and firm. Cool on a wire rack.
In a small saucepan bring whipping cream just to boiling over medium-high heat. Remove from heat; add chocolate pieces (do not stir). Let stand 5 minutes. Stir until smooth. Pour chocolate mixture evenly over the bottom of the crust.
For filling, in a medium saucepan combine brown sugar, cornstarch, and salt. Whisk in about 1/2 cup of the evaporated milk. Whisk in egg yolks until combined. Whisk in the remaining evaporated milk and the milk. Cook and stir over medium heat until thickened and bubbly. Remove from heat. Stir in the 3 tablespoons butter and the vanilla. Cover and keep warm.
Prepare Brown Sugar Meringue. Pour warm filling into prepared piecrust. Spread meringue over warm filling, sealing to edge of crust and swirling meringue into peaks. Bake for 15 minutes or until meringue is firm and golden. Cool on a wire rack for 1 hour. Chill for 4 to 6 hours before serving; cover for longer storage.
Brown Sugar Meringue
In a large mixing bowl beat egg whites with an electric mixer on medium speed until soft peaks form (tips curl). Gradually add brown sugar and granulated sugar, 1 tablespoon at a time, beating on high speed until stiff peaks form (tips stand straight) and sugar dissolves.