01 - Preheat oven to 350°F and grease a 9x13-inch baking pan with butter or nonstick spray.
02 - Prepare brownie batter according to package instructions. Pour into prepared pan and bake 25-30 minutes until toothpick inserted in center comes out with moist crumbs. Cool completely, then cut into 1-inch cubes.
03 - Whisk together pistachio pudding mixes and cold milk in large bowl for 2 minutes until thickened. Add food coloring if desired. Refrigerate until ready to assemble.
04 - In chilled bowl, beat heavy cream, powdered sugar and vanilla extract with electric mixer until stiff peaks form.
05 - In trifle dish or glass bowl, layer half the brownie cubes, half the pistachio pudding, then half the whipped cream. Repeat layers with remaining ingredients.
06 - Sprinkle top with green sprinkles, chocolate shavings or chopped pistachios if using.
07 - Refrigerate at least 2 hours before serving for best flavor and texture.