Walnut Baklava

Name: Walnut Baklava
Ingredients: 2 1/4 cups finely chopped walnuts (about 15 ounces); 1 1/2 cups plus 3 tablespoons granulated sugar , divided; 1 teaspoon ground cardamom; 3/4 teaspoon kosher salt; 1 (16-ounce) package frozen phyllo sheets (such as Fillo Factory), thawed; 1 cup unsalted butter (8 ounces), melted; 3/4 cup water; 2 teaspoons rosewater; 1 teaspoon fresh lemon juice; Chopped pistachios (optional)