In a medium bowl, combine softened butter, brown sugar, all-purpose flour, and a pinch of salt to prepare streusel.

In a separate bowl, beat the cream cheese until smooth. Add the egg yolk and granulated sugar, mixing until fluffy to make the cheesecake layer.

Preheat your oven to 425°F (220°C) and prepare a muffin tin by lining it with paper liners.

In a large bowl, cream softened butter with sugars until light and fluffy, then mix in eggs, yogurt, and vanilla extract.

In another bowl, whisk together the all-purpose flour, baking soda, baking powder, and salt, then fold into the wet mixture.

Fold in the frozen mixed berries gently to the batter.

Fill each muffin cup with batter, add a spoonful of cheesecake mixture, then top with muffin batter and streusel.

Bake at 425°F for 5 minutes, then reduce to 350°F and continue for 15-18 minutes, or until golden brown.