In a medium bowl, mix together 1 cup of flour, 1/2 cup of light brown sugar, and a pinch of salt with a fork until well combined. Next, drizzle in 1/4 cup of melted unsalted butter, then stir until the mixture resembles coarse crumbs. Set this aside.

In a separate bowl, blend 8 ounces of softened cream cheese with 1/4 cup of granulated sugar, 2 tablespoons of cornstarch, and 1 teaspoon of vanilla extract until smooth and creamy.

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 fully incorporated. In another bowl, whisk 1 large egg with 3/4 cup of granulated sugar until pale and fluffy.

Gradually stir in 1 cup of Greek yogurt and 1/4 cup of melted unsalted butter, followed by 1 teaspoon of vanilla extract to create a smooth batter.

Gently fold the wet mixture into the dry ingredients, mixing just until combined. Add 1 cup of mixed berries to the batter and gently stir to distribute.

Spoon the batter into lined muffin cups, filling each about 2/3 to 3/4 full. Create a small well in the center of each cup and spoon in the cream cheese filling. Top with a few additional berries and sprinkle the streusel topping over the top.

Preheat your oven to 350°F (175°C). Bake for 30-35 minutes or until golden brown and a toothpick inserted comes out clean.

Allow the muffins to cool in the pan for 5-10 minutes before transferring to a wire rack. Mix 1 cup of powdered sugar with a teaspoon of milk until smooth and drizzle over cooled muffins.