In a mixing bowl, combine 1/2 cup of all-purpose flour, 1/4 cup of granulated sugar, and a pinch of salt. Pour in 1/4 cup of melted unsalted butter, then mix until coarse crumbs form. Set aside.

In another bowl, beat together 8 ounces of softened cream cheese and 1/4 cup of granulated sugar until smooth. Add 1 tablespoon of cornstarch and 1 teaspoon of vanilla extract, mixing until incorporated.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 2 teaspoons of baking powder, and 1/2 teaspoon of salt until combined. Set it aside.

Combine 1 large egg, 3/4 cup of granulated sugar, 1 cup of Greek yogurt, 1/4 cup of melted unsalted butter, and 1 teaspoon of vanilla extract. Whisk until creamy.

Gently fold the wet ingredients into the dry mixture until combined, then fold in half of the mixed berries.

Line a muffin tin with liners or grease it lightly. Spoon 1½ tablespoons of batter into each cup. Add about 1 tablespoon of cream cheese filling, then top with remaining berries.

Sprinkle the streusel mixture over each muffin and press down gently to adhere.

Preheat the oven to 375°F (190°C). Bake for 30-35 minutes, lowering the temperature to 350°F (175°C) after 5 minutes.

Allow the muffins to cool for 5-10 minutes, then transfer to a wire rack. For glazing, mix 1 cup of powdered sugar with 2-3 tablespoons of milk until smooth and drizzle over the cooled muffins.