Start by preparing the streusel topping by mixing together brown sugar, flour, and salt in a small bowl.
Once combined, add the melted butter and stir until it forms a crumbly texture. Set this aside for later.
Next, make the muffin batter by whisking flour, baking powder, and salt in a large bowl.
In a separate bowl, mix together sugar, egg, vanilla, and melted butter until well combined. Stir in sour cream and milk, then gently fold in the fresh strawberries, making sure not to crush them.
For the cream cheese filling, blend softened cream cheese, sugar, vanilla, and cornstarch in a separate bowl until smooth and creamy.
To assemble the muffins, line your muffin tin with paper liners.
Spoon two-thirds of the muffin batter into each cup.
Add a spoonful of the cream cheese filling in the center of each muffin, then cover with the remaining muffin batter. Don’t worry about perfection, it’s all part of the charm!
Top each muffin with the streusel mixture, spreading it evenly over the batter.
Pop the tin in a preheated 350°F (175°C) oven and bake for 20 minutes, until golden brown on top and a toothpick inserted into the center comes out clean (or with a few crumbs, but no wet batter).
Let the muffins sit in the tin for a few minutes, then carefully transfer them to a wire rack to cool fully. Enjoy!