In a medium mixing bowl, add the flour, sugar and salt. Whisk to combine well.

Pour the melted butter into the dry mixture and mix with a fork until well combined, and the mixture resembles sand. Set aside.

Add the melted butter, white sugar, eggs, buttermilk, sour cream and vanilla to a large mixing bowl, and beat with a whisk until it has formed a smooth consistency.

In a separate bowl, add the flour, baking powder, baking soda, and salt. Whisk until well combined, then add this dry mixture to the wet mixture. Mix with a wooden spoon, until just combined, ensuring not to over mix. Fold in the raspberries.

Cover the muffin batter and place into the fridge to rest for 4 hours to overnight.

Preheat oven to 425°F. Prepare a cupcake tin with liners.

Evenly disperse the batter into the cupcake liners with a medium cookie scoop while being careful not to deflate the batter.

Sprinkle the streusel topping on top of each muffin. Place into the 425°F oven, bake for 6 minutes, and then turn the oven temperature down to 350°F, and bake for an additional 12 minutes, or until an inserted toothpick comes out clean.