Prepare Crumb Topping: In a medium bowl, combine flour, light brown sugar, and a pinch of salt. Melt the unsalted butter and pour it into the bowl, mixing with a fork until coarse crumbs form.

Make Cream Cheese Filling: Blend softened cream cheese with granulated sugar, cornstarch, and vanilla extract until smooth.

Mix Dry Ingredients: Sift together all-purpose flour, baking powder, and salt in a large bowl.

Combine Wet Ingredients: Whisk together egg and granulated sugar until pale and frothy, then add Greek yogurt, melted butter, and vanilla extract, folding until smooth.

Add Berries: Gently fold in half of the blueberries and raspberries into your muffin batter.

Assemble Muffins: Fill muffin cups with batter, create indentation for cream cheese filling, spoon in mixture, top with berries, then fill again with more batter.

Add Streusel Topping: Sprinkle prepared crumb topping over each muffin.

Bake: Preheat oven to 350°F (180°C) and bake for 30 to 35 minutes until golden and a toothpick comes out clean.

Cool: Allow muffins to cool in the pan for 5 to 10 minutes before transferring to a cooling rack.

Prepare Glaze: Combine powdered sugar with milk until desired consistency is reached, then drizzle over cooled muffins.