Lightly spray an 8-inch pie plate with non-stick cooking spray. Fit pie crust into the bottom and up sides of pie plate; set aside.
Melt butter and chocolate together in a small saucepan over very low heat, stirring frequently. Remove from heat and immediately add sugar; stir until well combined. Allow to stand about 3 minutes to cool slightly.
Place eggs in a mixing bowl; beat lightly with a fork or whisk. Add chocolate mixture and whisk until well combined.
Pour into crust.
Bake at 350 degrees on the bottom oven rack for 30 minutes. Move to top oven rack and bake for 10 minutes more. Cool to room temperature.
Serve with a dollop of whipped cream, if desired.