Preheat your oven to 350°F (175°C). Grease an 8-inch square baking dish with butter, then line it with parchment paper.

In a large mixing bowl, combine 1 cup of finely ground pistachios, 1 cup of all-purpose flour, and 3/4 cup of sugar. Stir until well-mixed.

Add 3 large eggs one at a time to the dry mixture, beating each until fully incorporated.

Melt 1/2 cup of butter and allow to cool slightly before folding it into the pudding batter.

Pour the batter into the prepared dish and bake for 25-30 minutes until golden brown and a toothpick comes out clean.

While the pudding bakes, prepare the cream sauce by combining 1 cup of cream, 1/2 cup of pistachio paste, and 1/4 cup of white chocolate over low heat. Stir until smooth.

Once cooled, slice the pudding into squares and serve with the pistachio cream sauce.