Preheat oven to 425°F / 220°C and line a muffin tray with paper cases of your choice
Make the Crumb Topping
Melt the butter in the microwave
Put flour and sugar in a bowl and mix together
Gradually add the melted butter to the flour/sugar mix a little at a time while stirring with a fork until clumps form. You should have a soft and crumbly mix with various sizes of clumps.
Break apart the clumps so they are as big or as small as you want them and then set aside until you are ready to put on top of the muffins
Make the Muffin Batter
In a large bowl, whisk together eggs and sugar
Mix in sour cream, oil and vanilla extract
In a separate bowl, sieve together the flour, baking powder, and salt. Add to the muffin batter and whisk until there are no lumps.
Fold in the raspberries, don't worry if they color the batter a little pink!
Scoop batter into muffin tray and top generously with the crumb topping.
Bake for 5 minutes at 425°C / 220°C, then turn the oven temperature down to 350°F / 180°C and bake for a further 13 - 15 minutes. When they are done, they should be golden brown on top and a skewer inserted should come out clean or with moist crumbs.
Let cool in the muffin pan for 10 minutes before transferring to a wire rack to cool completely.
Notes
Fresh or Frozen raspberries. You can use either fresh or frozen raspberries, I like to use frozen if it's not raspberry season as the quality and flavor tend to be a little better. Make sure you defrost your raspberries completely before adding them to the muffin batter. Be gentle when you fold them in. Pro Tip: If you find that your muffin cases often stick to your muffins, try spraying them lightly with cooking spray before adding the batter, this will help them to peel away easily.