Step 1 / 10
Preheat the oven to 180 °C. Line a muffin tin with paper liners.
Step 2 / 10
In a large bowl, whisk together the soft butter, sugar, salt, and vanilla until smooth and creamy.
Step 3 / 10
Add the eggs one at a time, whisking well after each addition.
Step 4 / 10
In a separate bowl, mix the flour and baking powder.
Step 5 / 10
Add one-third of the flour mixture to the butter mixture and stir. Add half of the milk and mix. Repeat with another third of the flour, the remaining milk, and finally the last third of the flour. Mix until just combined.
Step 6 / 10
Add the blueberries to the dough and mix them in.
Step 7 / 10
Make the streusel: In a small bowl, combine the cold butter cubes, brown sugar, flour, and salt. Rub the mixture between your fingers until it forms coarse crumbs.
Step 8 / 10
Divide the batter evenly among the muffin cups. Generously sprinkle the streusel over each muffin.
Step 9 / 10
Bake for 20-25 minutes.
Step 10 / 10
Let cool completely and enjoy!