Preheat and prepare. Set your oven to 180°C (350°F) and line a 12-hole muffin tin with paper liners. The kitchen should feel warm, and the liners should sit snugly in the tray.

Whisk the dry ingredients. In a large mixing bowl, combine the almond flour, erythritol, baking powder, and salt. Whisk them together until the mixture looks uniform and pale, with no obvious clumps of baking powder remaining.

Mix the wet ingredients. In a separate small bowl or jug, whisk the eggs, melted butter, vanilla extract, and almond milk. The mixture should look glossy and slightly thickened, with a smooth, pale yellow colour.

Combine wet and dry. Pour the wet mixture into the dry ingredients. Stir with a rubber spatula until just combined. The batter will look thick, almost like a cookie dough, and will have a slightly grainy texture from the almond flour. Do not overmix — stop the moment you see no dry streaks.

Fold in the berries. Gently fold the blueberries and lemon zest (if using) into the batter. Use a light hand; you want to hear a soft squelch as the berries break slightly, but not so much that the batter turns purple. The batter should now be studded with bright blue pockets.

Rest the batter. This is a crucial step. Let the batter sit on the counter for 5 minutes. You will see it thicken further as the almond flour absorbs the moisture. This rest ensures the muffins don't spread too flat.

Fill the liners. Divide the batter evenly among the 12 liners. Use a small ice cream scoop or two spoons. The batter should fill each liner about three-quarters full. The tops will look slightly domed and rough.

Bake until golden. Bake for 20 to 22 minutes. At the 18-minute mark, the kitchen will smell wonderfully nutty and sweet. The muffins are done when the tops are a deep golden brown, and a skewer inserted into the centre comes out clean or with just a few moist crumbs. The edges will have pulled away slightly from the paper liners.

Cool completely. Transfer the tin to a wire cooling rack and let the muffins cool for 10 minutes in the tin. Then, lift them out and let them cool fully on the rack. They will feel fragile when warm but will firm up as they cool. The texture should be tender and moist, not gummy.