In a medium bowl, combine ½ cup of all-purpose flour, ¼ cup of granulated sugar, and a pinch of salt. Drizzle in ¼ cup of melted unsalted butter, mixing with a fork until coarse crumbs form. Set aside.

In a separate bowl, beat together 8 ounces of softened cream cheese, ¼ cup of granulated sugar, 1 tablespoon of cornstarch, and 1 teaspoon of vanilla extract until smooth and creamy. Set aside.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 1 tablespoon of baking powder, and a pinch of salt. In another bowl, combine 1 egg with ¾ cup of granulated sugar, then add ¾ cup of Greek yogurt, ⅓ cup of vegetable oil, and 1 teaspoon of vanilla. Pour the wet ingredients into the dry ingredients and mix until just combined.

Gently fold in 1 cup of blueberries and 1 cup of raspberries, preserving their shape. Reserve a handful of berries for topping.

Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners. Spoon about 2 tablespoons of muffin batter into each liner and fill the center with the cream cheese mixture. Top with reserved berries and crumb topping.

Bake for 30 to 35 minutes, or until the tops are golden brown and a toothpick comes out clean. Keep an eye on the muffins while baking.

Once baked, let the muffins cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

Prepare a glaze by mixing 1 cup of powdered sugar with 2 tablespoons of milk until you reach your desired consistency. Drizzle over cooled muffins.