In a bowl, combine all the crumble ingredients using a fork until the mixture has a sandy, crumbly texture. Avoid overmixing. Set it aside while you prepare the muffin batter.

Preheat your oven to 200°C (fan or static).

Line your muffin tin with paper cases to prevent sticking and make removal effortless.

In a large bowl, sift together the flour, baking powder, bicarbonate of soda, and salt.

Sifting helps remove lumps and aerates the flour, ensuring light, fluffy muffins.

In a separate bowl, lightly whisk the egg until smooth.

Add the brown sugar and mix well until the sugar begins to dissolve.

Stir in the buttermilk, lemon zest, and vanilla extract for added flavor.

Finally, mix in the cooled melted butter until everything is fully combined.

Gradually add the dry ingredients to the wet mixture in three batches, stirring gently each time.

Be careful not to overmix; the batter should remain slightly lumpy for tender, moist muffins.

Gently fold in 50 g of fresh or frozen blueberries using a spatula. Mix just enough to distribute them evenly without breaking them.

Fill each muffin case 3/4 full with batter.

Generously sprinkle the prepared crumble on top for a delightful crunch.

Bake at 200°C for 10 minutes.

Lower the oven temperature to 180°C and bake for an additional 15 minutes.

To check doneness, insert a toothpick into the center of a muffin—it should come out clean or with a few moist crumbs. If needed, bake for another 5 minutes.

Remove the muffins from the oven and let them cool in the tin for 5 minutes.

Transfer them to a wire rack to cool completely before enjoying these golden, crumbly delights!