Preheat your oven to 350°F.
Spray a 12-count muffin tin with nonstick cooking spray or line it with paper muffin liners.
Using a stand mixer or hand mixer, cream together the softened butter and sugar on medium speed for about 2 minutes, until light and fluffy.
Reduce the speed to low and add the eggs. Add the vanilla extract and mix until fully incorporated.
Add the sour cream and continue mixing until smooth.
Next, add the baking powder and salt and mix well.
Gradually add the flour, mixing just until combined.
Gently fold in the frozen blueberries. Be careful not to overmix.
In a small bowl, combine the cold butter pieces, sugar, and flour.
Use a fork to work the ingredients together until a crumbly streusel forms.
Divide the muffin batter evenly among the 12 muffin cups.
Sprinkle the streusel topping evenly over each muffin.
Bake for 25–28 minutes, or until the tops are lightly golden.
Allow the muffins to cool in the pan for about 5 minutes before transferring them to a wire rack.
Serve warm or at room temperature.