Preheat and Prepare: First, preheat your oven to 180°C (160°C fan). Grease and line a 23cm (9-inch) square baking tin with baking parchment, leaving some overhang to help you lift the bars out later.

Mix Dry Ingredients: In a large mixing bowl, whisk together the plain flour, light brown sugar, baking powder, salt, cinnamon, and nutmeg. Breaking up any lumps of brown sugar is key here.

Mix Wet Ingredients: In a separate medium bowl, whisk the egg, buttermilk, melted butter, and vanilla extract until well combined and smooth.

Combine Gently: Pour the wet ingredients into the dry ingredients. Using a spatula, fold everything together until just combined. Be careful not to overmix; a few little lumps in the batter are perfectly fine. Over-mixing can make the bars tough.

Bake the Bars: Spread the batter evenly into your prepared tin. I find an offset spatula works best for this. Bake for 22-25 minutes, or until the top is golden brown and a skewer inserted into the centre comes out clean.

Cool Slightly: Let the baked base cool in the tin on a wire rack for about 15-20 minutes. It should be just slightly warm to the touch before you add the glaze.

Make the Glaze: While the base is cooling, prepare the glaze. In a medium bowl, whisk together the sifted icing sugar, maple syrup, 2 tablespoons of milk, and vanilla extract until smooth. If the glaze is too thick, add the remaining tablespoon of milk until it reaches a pourable, but not watery, consistency.

Glaze and Set: Pour the glaze evenly over the slightly warm base. Gently tilt the tin to help it spread to the edges. Let the glaze set completely at room temperature, which can take about 1-2 hours, before lifting the slab out of the tin and slicing into 16 bars.