1-First Step: Preheat your oven to 350°F and grease a 9×13-inch pan with butter or non-stick spray. This sets up for even baking of your birthday sugar cookie bars. Measure all ingredients ahead to keep things smooth.

2-Second Step: In a large bowl, cream together 1 cup softened butter and 1.5 cups sugar using a hand mixer until light and fluffy, about 2-3 minutes. This builds air into the dough for soft sugar cookie bars birthday texture. Scrape down sides for even mixing.

3-Third Step: Beat in 2 eggs one at a time, followed by 1 tsp vanilla extract. Mix until fully combined. For vegan adaptations, use flax eggs here to maintain binding without dairy.

4-Fourth Step: In a separate bowl, whisk together 2.5 cups flour, 1 tsp baking powder, and ½ tsp salt. Gradually add dry ingredients to wet mixture on low speed. Stir just until a thick dough forms, avoiding overmixing for tender cookie bars recipe results.

5-Fifth Step: Spread the dough evenly into the prepared pan using a spatula. Press down firmly for uniform thickness in these easy sugar cookies. Bake for 20-25 minutes until edges turn golden brown. Centers stay soft, perfect for party cookie bars.

6-Sixth Step: Remove from oven and cool completely in the pan on a wire rack, about 1 hour. This prevents crumbling when frosting your frosted birthday cookie bars.

7-Seventh Step: For frosting, beat ½ cup softened butter until creamy. Gradually add 3 cups powdered sugar, 2-3 tbsp milk, and 1 tsp vanilla. Adjust milk for spreadable consistency. Tint with gel food coloring for birthday themes.

8-Eighth Step: Spread frosting evenly over cooled bars. Add sprinkles immediately for fun toppings on no bake sugar cookie bars birthday style treats. Though baked, they assemble quickly.

9-Final Step: Chill in fridge for 30 minutes to set frosting, then slice into 24 bars. Serve on a platter for parties. These steps yield perfect birthday sugar cookie bars every time, with room for gluten-free flour or low-cal tweaks in mixing.