Preheat your oven to 200°C (180°C fan) and line a 12-hole muffin tin with paper cases. The cases will feel flimsy and light in your hand, but they hold their shape once filled.

In a large mixing bowl, whisk together the flour, caster sugar, baking powder, bicarbonate of soda and salt. The mixture should look pale and powdery, with no lumps visible when you lift the whisk.

Make a well in the centre of the dry ingredients and pour in the vegetable oil, Greek yoghurt, eggs, lemon zest, lemon juice and vanilla extract. Stir gently with a wooden spoon until just combined — you want a thick, bumpy batter that smells sharply of lemon. Stop stirring the moment you no longer see streaks of flour; overmixing will make the muffins tough.

Fold in the blueberries with a silicone spatula, using no more than ten turns. You should see purple streaks bleeding into the batter, and the berries will be evenly distributed but not crushed.

For the streusel, rub the cold butter cubes into the flour, brown sugar and cinnamon using your fingertips until the mixture resembles rough breadcrumbs. When you squeeze a handful, it should clump together briefly before falling apart again.

Divide the muffin batter evenly among the 12 paper cases — each case should be about three-quarters full. The batter will feel thick and slightly sticky, almost like a soft cookie dough.

Sprinkle the streusel topping generously over each muffin, pressing it down ever so lightly with your fingers so it sticks to the batter. You should see a thick, crumbly layer covering the surface.

Bake for 18-20 minutes, rotating the tin halfway through. The muffins are ready when the tops are deep golden brown, the streusel looks crunchy and set, and a skewer inserted into the centre of a muffin comes out with just a few moist crumbs attached — no wet batter.

Let the muffins cool in the tin for 5 minutes — you will hear a faint crackling sound as the sugar in the streusel sets — then transfer them to a wire rack to cool completely. The tops should feel firm but give slightly when pressed.