Prepare pistachio praline: Heat the roasted whole pistachios in a frying pan or microwave until fragrant and warm. Transfer to a food processor and pulse to break down.
Make pistachio paste: Add sunflower oil to the pistachios in the food processor and blend until smooth. Melt the unsalted butter and pour it into the processor while blending to create a smooth pistachio praline paste.
Mix mosaic base: In a bowl, whisk together the melted white couverture and sweetened milk until combined. Add the pistachio praline paste and mix well.
Prepare cookies: Crush the Bear-type cookies coarsely. Pour cognac over the crushed cookies if using alcohol. Add a pinch of salt and mix.
Combine mosaic mixture: Add the cookie mixture to the pistachio and chocolate mixture and stir until evenly combined and thickened.
Set the mosaic: Pour the mixture onto a baking sheet lined with parchment paper. Wrap and close the edges like candy. Refrigerate for 4 to 5 hours to firm up (or bake in oven for 2 to 3 hours as an alternative).
Serve: Remove from fridge, unwrap, cut into pieces, and serve garnished with finely chopped pistachios. Optionally drizzle with white chocolate and sprinkle additional pistachios for presentation.