Cut a sheet of parchment or aluminum foil 8-inches wide and long enough to extend above the pan on two sides. (This will make it easier to remove the bars from the pan before cutting them. It makes for better and more even cuts.)
Toast the pecans for the crust and the filling by placing in a frying pan over medium-low heat. Heat gently for approximately 5 minutes, stirring frequently to prevent burning. The nuts should begin to smell fragrant when they are ready. Remove from heat immediately and place nuts in a bowl to prevent any further cooking.
Crust:
If using a food processor, place 1/2 of the toasted nuts in the processor bowl. Pulse until the nuts are very finely chopped. Add flour, brown sugar, and salt and pulse until the ingredients are thoroughly mixed.
With the food processor running on low speed, add lumps of the softened butter and mix until incorporated and crust mixture becomes a similar texture throughout. It will be somewhat stiff.
If you are not using a food processor, beat the butter until smooth with an electric mixer. Add the brown sugar and beat until thoroughly mixed. Add the flour, finely chopped nuts and salt and stir until a stiff dough is formed.
Spread over parchment paper in prepared pan, and press down firmly to create an even crust. .Bake for 15 minutes.
While crust is baking, prepare the filling.
Filling:
Heat butter and brown sugar together over medium-low heat until the butter has melted.
Stir the mixture until the butter is evenly mixed with the sugar. Heat until it starts to bubble. Let cook for 1-2 minutes, stirring constantly.
Add the salt and whipping cream. Heat until the mixture is bubbling again. Cook for 4-5 minutes. The color of the mixture should begin to darken a bit, and it should thicken slightly. Remove from the heat and let cool for 5 minutes.
Add 1/4 cup of the cooled cream mixture to the beaten eggs and stir quickly until completely mixed.
Pour the egg into the remaining cream mixture and stir thoroughly.
When the baked crust is removed from the oven, let it cool for 5 minutes, then sprinkle with the chopped pecans and butterscotch chips. Pour the the cream mixture over the crust and return to the oven for 25 more minutes, or until the filling has firmed and the crust is lightly browned.
Remove from the oven and let cool completely in the pan.
While the bars are cooling, prepare the topping.
Topping
Place the chocolate in a small mixing bowl.
If you are using the orange rind, add it to the cream and let the mixture sit for 5-10 minutes.
Heat the cream to boiling point in microwave or on stove top.
Pour hot cream over chocolate. If you are using the orange rind, pour the cream through a strainer to remove the rind.
Let chocolate sit for 5 minutes so that the heat of the cream can melt the chocolate.
After five minutes, stir until the chocolate becomes smooth and glossy. If there are still a few unmelted lumps remaining, heat mixture in microwave for 30 seconds, or place bowl over a pan of simmering water and stir until smooth.
Put the chocolate aside until the bars are completely cool. Spread chocolate over cooled bars. (You can heat cooled chocolate for 30 seconds so that it will pour more easily.)
Let chocolate set (you can refrigerate the bars to speed this process up).
When ready, loosen edges of bars, then lift out with the parchment paper.