Preheat your oven to 375°F (190°C). While that’s heating up, greasing a 9x13-inch baking pan is crucial so your bars come out cleanly. A spritz of cooking spray or a layer of softened butter works great. Just don’t skip this part; no one likes bars that stick!

In a medium mixing bowl, blend together 3 cups of all-purpose flour, 1 cup of granulated sugar, and 1 teaspoon of baking powder. If you enjoy a hint of warmth in your dessert, now's the time to mix in a pinch of ground cinnamon and a dash of salt. Whisk until everything is well-combined.

Using a fork or a pastry cutter, work in 1 cup of softened unsalted butter until the mixture resembles coarse crumbs. Then, crack in 1 large egg and a teaspoon of vanilla extract. This adds a touch of sweetness and depth—just one of those little touches that elevates the flavor. Mix until all the ingredients hold together as a crumbly dough.

Take half of the crumbly dough and press it firmly into the bottom of your prepared pan. This will act as the base for your blueberry filling. Ensure it’s even and packed in well; it’ll give a solid foundation for those juicy blueberries.

In a separate bowl, combine the remaining ½ cup of granulated sugar and 3 teaspoons of cornstarch. Add the 4 cups of fresh blueberries and toss gently to coat. The sugar and cornstarch will create a luscious filling as it bakes, so don’t rush this step!

Spread the blueberry mixture evenly over the crust you’ve just created. Then, crumble the remaining dough you initially set aside on top of the blueberries. This sweet topping will create that lovely contrast in texture once baked.

Put your assembled blueberry bars into the preheated oven. Bake until the top is slightly golden-brown, which should take about 45 minutes. Your kitchen will smell heavenly during this time!

Once done, allow the bars to cool completely in the pan. This cooling step is essential to achieve nice, neat cuts. When you're ready for a taste, cut them into squares and marvel at your creation.