Preheat oven to 325°. In a small saucepan, bring cream to a simmer. Remove from heat and add chocolate. Stir until chocolate is completely melted. Let sit 5 minutes. Stir in egg yolk until thoroughly combined.
Pour into pastry shell and bake until center of tart is just starting to firm up, about 25 minutes. Let cool to room temperature.
Note: Nutritional analysis is per serving.