Preheat your oven to 200°C (180°C fan) and line a 12-hole muffin tray with paper cases. The oven should be fully up to temperature before the batter goes in, so the muffins rise quickly and form a rounded top.

In a large mixing bowl, whisk together the flour, caster sugar, baking powder, bicarbonate of soda and salt until evenly combined. The mixture should look pale and feel light, with no lumps of powder visible.

In a separate jug or bowl, combine the orange zest, orange juice, buttermilk, oil, eggs and vanilla extract. Whisk them together until the mixture is smooth and a uniform pale cream colour, with the zest evenly distributed.

Pour the wet ingredients into the dry ingredients and stir gently with a spatula or wooden spoon. Stop mixing as soon as the flour is incorporated — the batter will look slightly lumpy and a little thicker than cake batter, which is exactly what you want.

Add the cranberries and fold them in with just a few strokes. The berries should be scattered evenly through the batter, and you should still see some small lumps in the mixture. Over-mixing at this stage will make the muffins dense.

Divide the batter evenly between the 12 paper cases. Each case should be filled to about three-quarters full — the batter will mound up slightly in the centre.

Make the streusel topping by rubbing the flour, brown sugar and cold butter together between your fingertips until the mixture resembles coarse breadcrumbs with some small pea-sized butter pieces still visible. Sprinkle a generous teaspoon of streusel over each muffin.

Bake on the middle shelf for 20–22 minutes. The muffins are ready when the tops are a deep golden brown, the edges have pulled away slightly from the paper cases, and a skewer inserted into the centre of a muffin comes out clean or with just a few moist crumbs attached. The kitchen should smell distinctly of toasted orange and baked fruit.

Leave the muffins in the tray for 5 minutes — they will be very tender straight from the oven — then transfer them to a wire rack to cool completely. The tops will feel firm to the touch but the inside will stay soft and moist.