Preheat your oven to 350°F (180°C). Then, lightly grease a square baking pan (about 8x8 inches) and line it with parchment paper. The parchment paper will make it super easy to lift the finished flapjacks out of the pan.

In a large saucepan, combine the butter, demerara sugar, and golden syrup. Melt these ingredients together over low heat, stirring constantly. You want everything to be fully melted and combined into a smooth, glossy mixture. Don't let it boil – just a gentle simmer is perfect.

Once the butter mixture is ready, remove the saucepan from the heat. Add the rolled oats and the pinch of salt to the pan. Stir everything together really well, making sure all the oats are evenly coated in the buttery syrup. It might seem like a lot of oats at first, but keep stirring until it all comes together.

Pour the oat mixture into your prepared baking pan. Use a spatula or the back of a spoon to spread the mixture evenly and press it down firmly. You want a nice, compact layer. This helps the flapjacks hold their shape.

Bake in the preheated oven for 20-25 minutes. Keep an eye on them – they should be golden brown around the edges and slightly firm to the touch. The center might still be a little soft, and that's okay; they will firm up as they cool.

Let the flapjacks cool completely in the pan before cutting them into squares or bars. This is important because they're quite fragile when warm. If you try to cut them too soon, they might crumble. Once cool, use a sharp knife to cut them into your desired size.