Start by preheating your oven to 325°F (160°C). Grab an 8x8-inch square pan, grease it well, and line it with parchment paper, letting the edges hang over for easy lifting later.

In a big mixing bowl, stir together the rolled oats, flour, ground ginger, cinnamon, nutmeg, and baking soda. This will be the base of your batter, so make sure everything is evenly combined.

In a small saucepan, combine the butter, molasses, and dark muscovado sugar. Heat gently, stirring every so often, until the mixture melts together into a smooth, shiny syrup. Take it off the heat and set it aside to cool for a couple of minutes.

Pour the warm molasses mixture over the dry ingredients. Using a wooden spoon or spatula, stir until everything is well coated. The batter will start coming together as it absorbs the syrupy goodness.

Whisk the egg and milk together in a small bowl, then pour it into the batter. Stir until you have a thick, sticky mixture. It might seem a bit loose, but that’s exactly how it should be.

Scoop the mixture into your prepared pan and spread it out evenly, smoothing the top as best as you can. Pop it into the oven and bake for 50–55 minutes, or until the top feels firm and a toothpick inserted into the center comes out clean.

Let the parkin cool in the pan for about 15 minutes before lifting it out using the parchment paper. Place it on a wire rack to cool completely. For the best results, wrap it in parchment paper and leave it in an airtight container for 2–3 days to let the flavors deepen.