In a medium bowl, combine 1/2 cup of all-purpose flour, 1/4 cup of light brown sugar, and a pinch of salt. Pour in 4 tablespoons of melted butter, mixing with a fork until coarse crumbs form. Set the streusel topping aside.

In a separate bowl, blend 8 ounces of softened cream cheese with 1/4 cup of granulated sugar, 1 tablespoon of cornstarch, and 1 teaspoon of vanilla extract. Mix until creamy and smooth.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 2 teaspoons of baking powder, and a pinch of salt.

In another bowl, whisk together 1 large egg and 3/4 cup of granulated sugar until pale yellow and slightly thickened. Add 1 cup of Greek yogurt, 1/2 cup of vegetable oil, and 1 teaspoon of vanilla extract. Mix until well combined.

Gently fold the wet ingredients into the dry ingredients using a rubber spatula until just incorporated.

Gently fold in 1 cup of mixed berries into the batter.

Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners. Spoon the batter into each muffin cup halfway and add the cream cheese filling in the center. Top with reserved berries.

Sprinkle the prepared streusel topping over each muffin. Bake for 30-35 minutes or until golden brown and a toothpick comes out clean.

Remove the muffins from the oven and let cool in the pan for about 5 minutes before transferring to a wire rack. Optional: drizzle with a glaze made from powdered sugar and water.