Was it similar to this one from Recipelink although this doesn't put any Heath bars directly on the crust?
ENGLISH TOFFEE PIE

1 tablespoon plain, unflavored gelatin
1/4 cup cold water
1 cup milk
1/2 cup brown sugar
3 eggs, separated*
2 tablespoons butter OR margarine
1/2 pound English toffee, coarsely ground
1 cup heavy cream, divided use
1 (9 inch) baked pastry shell or graham cracker shell (I like the graham cracker shell)

Soften gelatin in cold water 5 minutes.

Scald milk in top part of double boiler; add brown sugar mixed with well-beaten egg yolks; cook over boiling water until thickened, stirring constantly.

Remove from heat; add gelatin, butter, and vanilla, mixing well; set aside to chill.

When almost stiff, fold in two stiffly beaten egg whites* and half of the English toffee.

Beat 1/2 cup cream until stiff and fold into mixture. Pour filling into pie shell and chill until firm.

When ready to serve, beat remaining 1/2 cup cream until stiff; fold in the remaining egg white, beaten stiff* and spread over pie. Sprinkle with the remaining English toffee and serve at once.

Source: Sunset Cookbook of Favorite Recipes