Preheat and prepare your tin. Preheat your oven to 175°C (350°F). Line a 20cm square baking tin with parchment paper, leaving some overhang on two sides. This will act as handles later. The paper should look crisp and clean, not greasy yet.

Mix the wet ingredients. In a large bowl, whisk the melted butter with both sugars until combined. The mixture will look like a thick, grainy paste and smell wonderfully buttery. Add the eggs one at a time, whisking vigorously after each until the batter is smooth and glossy. Stir in the vanilla extract. The batter should feel thick and look almost like a caramel sauce.

Add the zucchini. Fold in the grated zucchini using a spatula. Do not overmix; you just want to incorporate it evenly. The batter will suddenly look a bit looser and speckled with green. This is exactly what you want – the moisture from the zucchini is the secret to the fudgy crumb.

Combine the dry ingredients. Sift the flour, cocoa powder, baking powder, and salt directly into the bowl. Fold gently with the spatula until just a few streaks of flour remain. The batter will be very thick and smell deeply of chocolate. Finally, fold in the chocolate chips. The batter should be cohesive, dense, and look almost like a mousse.

Bake to perfection. Pour the batter into the prepared tin and spread it evenly with the spatula. It will be quite thick, so take your time to push it into the corners. Bake for 22-27 minutes. The top should look set and slightly cracked, and a skewer inserted into the centre should come out with a few moist crumbs attached, not wet batter. You’ll know it’s ready when the kitchen smells like a chocolate factory and the edges have just started to pull away from the paper.

Cool completely. Place the tin on a wire rack and let the brownies cool in the tin for at least 20 minutes. This is crucial. If you try to cut them warm, they will crumble. The brownies will continue to set as they cool. After 20 minutes, use the parchment overhang to lift the block onto the rack to cool completely.

Make the glaze. Once the brownies are completely cool, make the glaze. Place the chopped dark chocolate in a heatproof bowl. Gently warm the double cream and golden syrup in a small saucepan until it just begins to simmer – you'll see small bubbles around the edge. Pour the hot cream over the chocolate and let it sit for 1 minute. Then stir slowly until smooth and glossy. The glaze should be pourable but thick enough to coat the back of a spoon.

Glaze and set. Pour the glaze over the cooled brownie block and spread it evenly to the edges. Let it set at room temperature for about 15 minutes before slicing. For a cleaner cut, pop the glazed block in the fridge for 10 minutes. The glaze will firm up to a lovely, snappy shell.