Make the streusel first. In a small bowl, combine the flour, brown sugar, cinnamon and salt. Drop in the cold butter cubes and rub them into the dry ingredients using your fingertips. Stop when the mixture looks like coarse, damp breadcrumbs with some pea-sized butter lumps still visible. Pop the bowl into the fridge while you prepare the batter—this keeps the butter solid, which creates those lovely crunchy clusters.

Preheat the oven to 200°C (180°C fan) and line a 12-hole muffin tin with paper cases. The high initial temperature is key for that dramatic muffin top.

Toss the blueberries in a small bowl with 1 tablespoon of flour until they are lightly coated. This simple step prevents them from sinking to the bottom of the muffins as they bake, ensuring a beautiful distribution of fruit throughout each cake.

Whisk the dry ingredients together in a large mixing bowl—flour, caster sugar, baking powder, bicarbonate of soda and salt. Give them a good stir until everything is evenly combined and you can see no lumps of bicarbonate.

In a separate jug or bowl, whisk together the eggs, oil, buttermilk, lemon zest, lemon juice and vanilla extract. The mixture should look pale yellow, slightly frothy on top, and smell wonderfully zesty and fresh.

Pour the wet ingredients into the dry and fold gently with a rubber spatula. Stop as soon as you see no more streaks of flour—a few small lumps are absolutely fine. Overmixing at this stage will make the muffins tough and dense. The batter should look thick, shaggy and slightly lumpy, like a rustic cake mix.

Fold in the floured blueberries with just two or three turns of the spatula. You want them evenly distributed but not crushed. If the batter begins to turn a faint purple colour, you have folded too vigorously—next time, go even gentler.

Divide the batter evenly among the 12 paper cases. The cases should be almost full, right up to the brim. This is not a time for timidity—a generous fill is what gives you that tall, professional-looking dome. Sprinkle the chilled streusel over each muffin, pressing it down lightly so it sticks.

Bake for 5 minutes at 200°C, then—without opening the door—reduce the oven temperature to 180°C (160°C fan) and bake for a further 17–20 minutes. The initial blast of heat sets the top quickly, while the lower temperature cooks the centre through. Your muffins are ready when they are golden brown, the streusel is crisp, and a skewer inserted into the centre of a muffin comes out with just a few moist crumbs attached—no wet batter.

Cool in the tin for 5 minutes, then transfer the muffins to a wire cooling rack. You will hear a gentle crackle as the streusel settles. Let them cool for at least 10 minutes before serving—the crumb needs that short rest to set properly, so you don’t end up with a handful of warm crumbs instead of a whole muffin.