Prepare the Pistachio Filling:

In a bowl, whisk together the instant pistachio pudding mix and cold milk until it thickens (about 2-3 minutes).
Gently fold in the whipped topping or whipped heavy cream for a light, creamy texture.
Refrigerate until ready to use.
Make the French Toast:

In a shallow bowl, whisk together the eggs, milk, vanilla extract, and cinnamon.
Heat a large skillet or griddle over medium heat and melt the butter.
Dip each slice of bread into the egg mixture, coating both sides.
Cook the bread slices in the skillet for 2-3 minutes per side, or until golden brown.
Assemble the Stuffed French Toast:

Take one slice of French toast and spread a generous layer of pistachio filling on top.
Place another slice of French toast on top to create a sandwich. Repeat with the remaining slices.
Serve and Garnish:

Dust the stuffed French toast with powdered sugar.
Add a dollop of whipped cream on top and sprinkle with crushed graham crackers for extra crunch.
Serve immediately and enjoy the creamy, nutty goodness!