Start by making the crumb topping: combine all the ingredients and a pinch of salt in a bowl and rub them together with your hands until you have a crumbly dough. You can also do this in a food processor, pulsing briefly until you have a crumbly dough. Then place the crumb topping in the refrigerator.

Now place the melted butter in a large bowl and mix it with the sugar.

Then add the eggs, buttermilk, Greek yogurt, and vanilla extract, and mix well.

Now add the (mixed) dry ingredients to the other bowl with the “wet” ingredients and mix until no flour remains. Don’t mix for too long; a brief mix is sufficient for muffins. If you mix the batter for too long, the muffins will become too dense and not light and fluffy.

Place the blueberries in a bowl with 1 or 2 tablespoons of flour until all the blueberries are well coated with a layer of flour. Then fold them into the batter.

Let the bowl sit for a moment and cover it with a tea towel while the oven preheats.

Meanwhile, preheat the oven to 220 degrees Celsius / 428 Fahrenheit with top- and bottom heat.

Line a muffin tin with parchment paper or cupcake liners.