Preheat an oven to 220 Celsius / 430 Fahrenheit / gas mark 7
Cream together the butter and sugars until light, pale and fluffy
Add in the eggs one at a time and whisk everything till well combined and fluffy (if the batter splits slightly here that's okay!)
Next, add in the vanilla and salt, mix well
Then, sift in the dry ingredients and fold in until fully combined
Pour in the milk and stir together
Coat the berries in a little flour before gently folding into the batter
Next, combine all the streusel ingredients in a bowl using a fork or your hands till you get breadcrumbs, or a wet sand like consistency
Finally, scoop out the batter into the muffin cases and sprinkle on the streusel before placing into the oven for 5 minutes then turning the heat down to 175 Celsius / 345 Fahrenheit / gas mark 3 for a further 18 - 20 minutes until fully cooked and golden, until a toothpick comes out clean
Allow the muffins to cool and enjoy!