Preheat the oven and prepare your tins. Set the oven to 200°C (180°C fan). Line a 12-hole muffin tin with paper cases — I prefer tulip-style cases for a taller, more elegant look. The paper should feel crisp and dry as you place them in the tin.

Make the streusel topping first. In a small bowl, combine 60g plain flour, 40g light brown sugar, and 30g rolled oats. Add the 50g cold cubed butter and rub it into the dry ingredients using your fingertips until the mixture resembles coarse, pale golden breadcrumbs. You should see small, distinct pebbles of butter throughout — this is what creates that shatteringly crisp texture. Pop the bowl into the fridge while you prepare the batter.

Whisk the dry ingredients together. In a large mixing bowl, sift together 300g plain flour, 200g caster sugar, 2 teaspoons baking powder, ½ teaspoon bicarbonate of soda, and ¼ teaspoon salt. The mixture should look pale and uniform, with no lumps. Set it aside.

Combine the wet ingredients. In a separate jug or bowl, whisk together 120ml oil, 2 eggs, 240ml buttermilk, 1 tablespoon lemon zest, 2 tablespoons lemon juice, and 1 teaspoon vanilla extract. The mixture will look slightly curdled from the lemon juice and buttermilk — that is perfectly fine and actually helps create a tender crumb. You should smell the bright, clean aroma of fresh lemon.

Fold the batter together gently. Pour the wet ingredients into the dry ingredients and use a rubber spatula to fold them together with just a few broad strokes. Stop as soon as you see a few streaks of flour remaining — overmixing will make the muffins tough. The batter should look thick, shaggy, and a little lumpy, not smooth.

Add the blueberries with care. Sprinkle the floured blueberries over the batter and fold them in with just two or three turns. You want the berries distributed evenly but not crushed; the batter should have visible pockets of deep purple and blue against the pale yellow background.

Fill the muffin cases and add the streusel. Divide the batter evenly among the 12 cases — each should be about three-quarters full. The surface should look slightly domed. Retrieve the streusel from the fridge and sprinkle a generous tablespoon over each muffin, pressing it down lightly so it adheres. The streusel should cover the top completely, with little buttery clumps peeking through.

Bake until golden and fragrant. Place the tin in the centre of the oven and bake for 22–25 minutes. At the 20-minute mark, the kitchen will fill with a warm, nutty, citrusy smell. The muffins are ready when the tops are deep golden brown, the streusel looks crisp and toasted, and a skewer inserted into the centre of a muffin comes out with just a few moist crumbs attached — no wet batter. The edges should be pulling away slightly from the paper cases.

Cool and serve with flair. Let the muffins rest in the tin for 5 minutes — they will feel fragile and steamy. Then transfer them to a wire cooling rack. The bottoms should sound hollow when tapped. Serve them slightly warm, when the streusel is at its most shatteringly crisp and the blueberries are still jammy and soft.