Preheat your oven to 350°F (175°C). Grease a round cake pan or a baking dish.
In a large bowl, combine the semolina, sugar, and baking powder. Mix well.
In another bowl, whisk together the milk, water, eggs, olive oil (or melted butter), vanilla extract, lemon zest, and orange zest.
Gradually add the wet ingredients to the dry ingredients, mixing until well combined.
Stir in the raisins, pine nuts, and chopped walnuts (if using).
Pour the batter into the prepared baking pan or dish.
Bake in the preheated oven for about 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Allow the Bustrengo to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Dust with powdered sugar before serving.
Enjoy your meal!