Preheat and prep your tin. Set your oven to 180°C (160°C fan) and line a 20cm square baking tin with a strip of parchment paper, leaving an overhang on two sides. This creates handy 'handles' for lifting the whole block out later. The paper should feel crisp and snug against the tin's edges.

Whisk the dry ingredients. In a large mixing bowl, sift together the flour, cocoa powder, bicarbonate of soda, and salt. Whisk briefly with a fork until the mixture is uniform and a deep, even brown colour. Set this bowl aside while you prepare the wet mixture.

Combine the wet ingredients. In a separate medium bowl, whisk the caster sugar, brown sugar, eggs, vegetable oil, and vanilla extract. Whisk vigorously for about a minute until the mixture becomes pale, thick, and glossy. You'll notice it lightens in colour and ribbons off the whisk when lifted. This aerates the batter and gives a lovely crackly top.

Fold in the courgette. Add the grated and squeezed courgette to the wet mixture and stir gently with a spatula. The courgette will look like it's swimming in the batter at first, but keep folding until it's evenly distributed. The mixture will seem looser than a typical brownie batter — that's exactly right.

Combine wet and dry. Pour the wet mixture into the bowl of dry ingredients and fold together using a rubber spatula. Use a gentle cutting and folding motion, scraping the bottom and sides. Stop as soon as you see no more streaks of flour; the batter should look thick, fudgy, and slightly lumpy. Overmixing will make the brownies tough, so work quickly.

Add the chocolate chips (if using). Fold in the dark chocolate chips until they're evenly scattered throughout the batter. You'll hear a soft clink as they knock against the bowl — that's the sound of promise.

Bake until just set. Pour the batter into the prepared tin and spread it evenly to the corners using the spatula. Bake for 25-28 minutes. At the 25-minute mark, insert a skewer into the centre — it should come out with a few moist crumbs clinging to it, not wet batter. The edges will have pulled away from the tin slightly and the top will look dry and cracked. A gentle press in the centre should feel springy but not firm.

Cool completely in the tin. Place the tin on a wire cooling rack and let the brownies cool completely in the tin. This is crucial — if you try to glaze them while warm, the glaze will slide straight off and pool at the bottom. The brownies will continue to set as they cool. Patience here is the hardest part.

Make the chocolate glaze. Once the brownies are cool, place the dark chocolate pieces in a heatproof bowl. Warm the double cream in a small saucepan over medium heat until it just begins to steam and tiny bubbles form around the edges — do not let it boil. Pour the hot cream over the chocolate and let it sit undisturbed for 2 minutes. Stir gently in one direction until the mixture is smooth, glossy, and thick enough to coat the back of a spoon. Stir in the golden syrup for extra shine.

Glaze and set. Pour the glaze over the cooled brownies and spread it evenly to the edges with a spatula. Let it sit at room temperature for about 20 minutes until the glaze is set but still has a slight give when pressed. For a neater slice, pop the tin into the fridge for 10 minutes before cutting. Lift the whole block out using the parchment handles, then slice into 16 squares with a sharp knife — you'll hear the glaze crackle as you cut through.