For the croutons:
1) Preheat the oven to 200C/Gas 6. In a medium bowl, toss together the bread cubes and melted butter. Add the vanilla sugar and toss until the bread cubes are coated in sugar. Arrange the bread cubes in a single layer on a parchment-lined baking sheet and bake until golden brown, about 8 to 10 minutes. Cool completely.
For the syrup:
1) In a small saucepan, bring the orange juice, lemon juice, and sugar to a simmer, over medium-low heat. Stir until the sugar has dissolved, about 2 to 3 minutes. Add the blueberries and strawberries and simmer until the fruit softens, about 6 to 8 minutes. Cool the syrup to room temperature.
For the Ricotta:
1) Combine all the ingredients in a medium bowl. Mix well.
To serve: Divide the ricotta mixture between 4 decorative dessert bowls. Spoon the fruit syrup over the ricotta and top with the croutons. Garnish with the sliced mint.
To make the vanilla sugar:
1) Place the sugar in the bowl of a food processor. Using a paring knife, slice the vanilla bean in half, lengthways, and scrape out the seeds. Add the vanilla seeds to the sugar. Pulse 10 to 15 times until the vanilla and sugar are combined. Cut the empty vanilla pod into 1-inch pieces and place in a glass mason jar. Add the vanilla sugar to the jar and seal. Shake the jar before using.