Preheat the oven to 350° and rub a pie dish with butter all over the bottom and up the sides.
Gently roll out the pie shell to about 12 inches and fit it over the pie dish. Carefully fit it into the bottom and sides of the pie dish and try not to break it. Fold and pinch the edges of the pie shell all along the perimeter of the dish.
Fit a sheet of aluminum foil or parchment paper into the pie dish and gently press it all over the bottom and sides of the pie crust. (Note: aluminum foil will be better because you can fold it lightly over the edges of the pie crust to keep it from getting too dark.)
Fill the inside with pie weights or dried beans and make sure it's spread evenly all over the crust.
Bake for about 25 minutes. Take the pie dish out of the oven and carefully remove the foil or parchment paper with the weights inside.
Poke a few holes over the bottom of the pie crust and a few on the sides and bake another 10-15 minutes. Take it out of the oven and make sure to cool completely before adding the filling.
Chocolate Pie Filling:
Chop the baking chocolate bar into small pieces and set aside.
EGGS: In a small, heavy-bottom sauce pot, over medium-low (to low) heat, whisk eggs and 1/2 cup of sugar together. Heat the eggs stirring slowly but constantly, until the mixture reaches 160° (F). This could take up to 10 minutes but don't walk away and don't stop slowly stirring or you will cook your eggs. Take off heat.
Add chocolate chunks into the hot egg mixture and slowly whisk and stir until chocolate is melted and incorporated. Set aside to cool completely.
WHIPPED CREAM: Using a cold whisk attachment, beat cold heavy cream in the cold bowl of an electric mixer, until stiff peaks appear. Place the whipped cream into the refrigerator until ready to use.
In an electric mixer, using a paddle attachment, beat butter and remaining 1/2 cup of sugar on medium-high speed until light and fluffy.
Slowly pour in cooled chocolate egg mixture (make sure that eggs and chocolate are no warmer than room temperature). Beat for 3-5 minutes, until smooth and silky.
Carefully, fold in the whipped cream until all evenly incorporated.
Transfer the pie filling into a cooled pie shell. Cover with plastic wrap and refrigerate for about 6 hours before serving.
Using a cold whisk attachment, beat cold heavy cream and 2 tbsp. of powdered sugar in the cold bowl of an electric mixer, until stiff peaks appear.
Spread whipped cream over the top of the cooled pie.
Shave a chocolate bar using a vegetable peeler over the top of the pie to get chocolate curls. If you want fine chocolate shavings, you can use a cheese grater to grate chocolate bar over the top.