To prepare a viennese nut squares desserts recipe, first you need to prepare the ingredients. First, you'll need the following ingredients: Preheat the oven to 375 degrees F (190 degrees C). Place the pistachios, walnuts and pecans in the bottom of an 8x8-inch baking pan. Bake the nuts for 10 to 12 minutes, or until they are lightly browned. Remove the pan from the heat and let cool for 5 minutes. Then, add the sugar and beat the mixture with an electric mixer until it's light and fluffy. Add the vanilla and mix until combined.