Creating berries and cream filled croissants can be straightforward if you follow these simple steps:

1. Thaw the Croissant Dough: Remove the croissant dough from the freezer and allow it to thaw according to package instructions.
2. Prepare the Cream Filling: In a mixing bowl, combine mascarpone cheese, heavy cream, powdered sugar, vanilla extract, and lemon zest (if using). Whip until smooth and creamy.
3. Prepare the Berries: Rinse the fresh berries gently under cold water. Pat them dry with a paper towel and set aside.
4. Preheat the Oven: Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.
5. Roll Out the Dough: Once the dough is thawed, roll out each croissant triangle on a lightly floured surface.
6. Fill the Croissants: Place a spoonful of the cream filling at the wider end of each triangle. Add a few berries on top of the filling.
7. Roll Up the Croissants: Starting at the wide end, roll the croissants towards the point, tucking the tip underneath.
8. Brush with Egg Wash: In a small bowl, beat the egg and brush the tops of the croissants with the egg wash for a golden finish.
9. Bake: Place the croissants on the prepared baking sheet and bake for 20-25 minutes, or until golden brown and flaky.
10. Cool: Remove the croissants from the oven and allow them to cool for 15-20 minutes.
11. Dust with Powdered Sugar: Before serving, dust the tops of the croissants with extra powdered sugar for an elegant touch.

These steps will guide you in creating these incredible croissants effortlessly.