Heat the oven and prepare the dish. Preheat the oven to 180°C (160°C fan / 350°F / Gas Mark 4). Grease a 23cm square baking dish generously with butter, getting right into the corners so nothing sticks. Set it aside on a baking tray — this catches any drips and makes the dish easier to move in and out of the oven.

Combine the dry ingredients. In a large mixing bowl, stir together the oats, baking powder, cinnamon and fine salt. You want an even, pale-tan mixture with no clumps of baking powder visible — if you spot any, press them out with the back of your spoon.

Whisk the wet ingredients. In a jug or a second bowl, whisk the eggs until they’re uniform and slightly frothy at the edges — about 30 seconds by hand. Add the milk, maple syrup, melted butter and vanilla, and whisk again until the mixture is glossy and pale gold. If you’re using orange zest, stir it in now.

Bring it together. Pour the wet mixture over the dry ingredients and stir with a spatula until every oat is coated. The mixture will look wet and loose — that’s exactly right. Fold in two-thirds of the chopped pecans, reserving the rest for the top.

Pour and top. Scrape the mixture into the prepared dish and level the surface with the back of your spatula. Scatter the remaining pecans across the top in an even layer. They should sit proud of the surface so they toast rather than sink.

Bake. Bake for 35–40 minutes. At the 30-minute mark, open the oven and take a look: the edges should be pulling away slightly from the sides and turning deep golden brown, while the centre should still have a faint wobble. The kitchen will smell of toasted nuts and warm cinnamon — that’s your cue that it’s nearly there. If the pecans are browning too fast, tent the dish loosely with foil.

Check for doneness. Insert a skewer into the centre. It should come out with a few moist crumbs but no wet streaks of batter. If it’s still liquid in the middle, give it another 5 minutes and check again.

Rest before serving. This is the step most people skip and it’s the one that makes the biggest difference. Leave the dish on a wire rack for 10 minutes. The residual heat finishes setting the centre, and the slices hold together beautifully when you serve them.

Finish and serve. Sprinkle with flaky sea salt and drizzle with a little extra maple syrup if you like. Scoop into bowls while warm, or cut into squares once fully cooled.