Preheat and Prepare: Preheat your oven to 180°C (160°C fan / Gas Mark 4). Grease and line a 20cm x 20cm square baking tin with baking parchment, leaving an overhang on two sides to easily lift the blondies out later. This preparation step ensures a seamless removal and minimal sticking, saving you time and effort.

Melt Butter and Combine Sugars: In a large mixing bowl, pour in the melted butter. Add the light muscovado sugar and caster sugar. Whisk them together vigorously until the mixture is glossy and well combined, taking on a slightly caramel-like hue and a wonderfully sweet aroma. This step is crucial for dissolving the sugars and creating that signature chewy blondie texture.

Add Wet Ingredients: Crack in the two large eggs, one at a time, whisking well after each addition until fully incorporated and the mixture looks pale and frothy. Stir in the vanilla extract and the tahini. Continue to whisk until the tahini is completely blended in, leaving no streaks, and the mixture becomes smooth and slightly thicker, emitting a faint nutty scent.

Incorporate Dry Ingredients: Sift the plain flour, baking powder, and salt directly into the wet mixture. Using a spatula or wooden spoon, gently fold the dry ingredients into the wet until just combined. Be careful not to overmix; stop as soon as you no longer see any pockets of dry flour. The batter will be thick and slightly lumpy, with a subtle bready aroma.

Fold in Chocolate Chips: Add the chocolate chips to the batter. Gently fold them through until evenly distributed. You want to see specks of dark and milk chocolate throughout the thick, rich batter. This ensures every bite gets a generous dose of chocolatey goodness.

Bake to Perfection: Pour the blondie batter into your prepared baking tin, spreading it evenly with your spatula. If desired, sprinkle a pinch of flaky sea salt over the top for a delightful contrast. Place the tin in the preheated oven and bake for 25-30 minutes. The blondies are ready when the edges are lightly golden brown and set, but the centre still has a slight wobble when gently shaken. A skewer inserted into the centre should come out with moist crumbs, not wet batter. The kitchen will fill with a heavenly warm, sweet, and nutty aroma.

Cool and Serve: Once baked, remove the tin from the oven and place it on a wire rack to cool completely in the tin. This is crucial for achieving that fudgy texture. Resist the urge to cut them while warm! Once cooled, use the parchment overhang to lift the blondie slab out of the tin. Cut into 12 squares. The blondies will be firm to the touch, with a slightly sticky, chewy exterior.