Slice the croissants in half and place on a lined baking sheet. Toast in the preheated oven for 5-10 minutes until golden and slightly crisp. Remove from the oven and let cool.
In a large mixing bowl, add the mascarpone, heavy cream, powered sugar, and vanilla bean paste. Use an electric mixer to whip until stiff peaks form.
Mix together the strawberries and raspberries in a separate bowl.
To assemble, spread or pipe a generous amount of the cream onto each croissant, and top with a spoonful or two of berries. Place the top half of the croissant on top and dust with powdered sugar. Serve immediately or chill in the fridge until ready to serve.