1. Preheat your oven to 350°F and prepare your baking pan by greasing it or lining it with parchment paper for easy removal.
2. In a large mixing bowl, cream together 1 cup (2 sticks) of softened butter and 1 cup of granulated sugar using a hand mixer or stand mixer on medium speed until the mixture is light, fluffy, and pale yellow.
3. Add 2 large eggs, one at a time, to the creamed butter mixture, blending well after each addition. Mix in 1 teaspoon of vanilla extract and 1/4 teaspoon of almond extract, if desired.
4. In a separate bowl, whisk together 2 1/2 cups of all-purpose flour, 1 (3.4 oz) box of pistachio instant pudding mix, 1 teaspoon of baking powder, and 1/2 teaspoon of salt. Gradually add the dry ingredients to the wet mixture, beating on low speed until fully combined. Scrape down the sides of the bowl as needed.
5. Spread the dough evenly into the prepared baking pan, ensuring an even thickness for uniform baking.
6. Bake in the preheated oven for 18–22 minutes, or until the edges are lightly golden and a toothpick inserted in the center comes out clean. Allow the bars to cool completely in the pan.
7. While the bars cool, prepare the cream cheese frosting by beating 4 oz of softened cream cheese and 1/4 cup of softened butter until smooth and creamy. Gradually mix in 2 1/2 cups of powdered sugar, 1/2 cup at a time, and finish with 1 teaspoon of vanilla extract and a pinch of salt.
8. Once the bars have cooled completely, spread the cream cheese frosting evenly over the top using a spatula.
9. Garnish with chopped pistachios, if desired, to add texture and a finishing touch.
10. Slice the frosted bars into squares or rectangles with a sharp knife and serve immediately, or store them in an airtight container for later.