1-First Step: Prepare the Streusel Topping: Begin by combining 6 tablespoons packed light brown sugar, 1/2 cup all-purpose flour, 1 teaspoon ground cinnamon, and 1/4 teaspoon salt in a small bowl. Use your fingers to mix until no lumps remain, then rub in 4 tablespoons of cold, cut unsalted butter until crumbly. Refrigerate this mixture until you’re ready to use it, which helps it stay firm for the perfect topping.

2-Second Step: Preheat and Prep the Pan: Heat your oven to 375°F (190°C) and position the rack in the middle for even baking. Grease a 9-inch square pan with butter or nonstick spray to prevent sticking. This step ensures your cake releases easily and bakes uniformly, typically taking about 5 minutes.

3-Third Step: Mix the Dry Ingredients: In a medium bowl, whisk together 2 cups all-purpose flour, 2 teaspoons baking powder, and 1/2 teaspoon salt. Set this aside as your dry base. For those with dietary needs, you can swap flour for a gluten-free option here to maintain the recipe’s structure.

4-Fourth Step: Cream the Butter and Sugar: Using an electric mixer, beat 1/2 cup softened unsalted butter and 3/4 cup granulated sugar until creamy, about 2 minutes. Add 2 large eggs one at a time, scraping the sides and beating well after each. Then, mix in 1 1/2 teaspoons vanilla extract and 1 teaspoon lemon zest for added flavor.

5-Fifth Step: Combine Wet and Dry Ingredients: Gradually add the dry mixture to the wet ingredients, alternating with 1/2 cup milk, while beating on low speed. Once combined, gently fold in 2 cups fresh blueberries with a spatula to distribute them evenly. Avoid over-mixing to keep the batter light; if adapting for a low-sugar diet, use applesauce as a substitute.

6-Sixth Step: Bake the Cake: Transfer the batter to your prepared pan and spread it evenly. Sprinkle the refrigerated streusel topping over the batter. Bake for 40-45 minutes until the edges turn golden and a cake tester comes out clean. Let it cool in the pan for about 20 minutes before serving, allowing flavors to settle.