Bake piecrust according to package directions. Cool on a wire rack.
Beat egg whites and cream of tartar at high speed with an electric mixer until foamy. Add 1/4 cup sugar, 1 tablespoon at a time, beating until stiff peaks form and sugar dissolves. Set aside.
Whisk remaining 1 cup sugar and next 3 ingredients in a small bowl. Whisk together egg yolks and milk in a separate bowl.
Melt butter in a 2-quart heavy saucepan over medium heat. Add sugar mixture to melted butter, whisking until blended. Gradually whisk in milk mixture. Cook, whisking constantly, until mixture is thickened and bubbly.
Remove from heat. Add chocolate morsels and vanilla, stirring until chocolate is melted. Stir in pecans. Cover and keep warm.
Pour hot filling into piecrust. Spread meringue over hot filling, sealing to edge of pastry.
Bake at 375° for 12 minutes or until golden. Cool completely on a wire rack. Store in refrigerator.
*For testing purposes only, we used Pillsbury Pet-Ritz frozen piecrust.
Tip: To avoid flattening out the meringue when you spread it on the filling, spoon meringue onto filling in large dollops; carefully connect the dollops with a light swirling motion.