Prepare Your Baking Tray: Preheat your oven to 175°C (160°C fan/Gas Mark 3). Line a 20x20cm (8x8 inch) square baking tray with parchment paper, leaving an overhang on the sides to easily lift the brownies out later. This small step saves so much time during cleanup, trust me.

Melt the Butter and Mix Sugar: In a large, microwave-safe bowl, melt the unsalted butter. Once melted, stir in the caster sugar until it's well combined and the mixture looks glossy and smooth. You'll notice the sugar crystals beginning to dissolve, creating a cohesive, slightly caramel-coloured base.

Add Wet Ingredients: Whisk in the eggs, one at a time, ensuring each egg is fully incorporated before adding the next. Then, stir in the vanilla extract. The mixture should become lighter in colour and slightly airy, with a distinct sweet, buttery aroma.

Combine Dry Ingredients: In a separate bowl, whisk together the plain flour, unsweetened cocoa powder, baking powder, and fine sea salt. Make sure there are no lumps of cocoa powder; it should be an even, light brown colour. This ensures an even distribution in the batter.

Fold in Dry Ingredients and Yoghurt: Gradually add the dry ingredients to the wet mixture, folding gently with a spatula until just combined. Be careful not to overmix; overmixing develops gluten, which can lead to tough brownies. The batter will be thick and slightly crumbly at first. Then, fold in the full-fat Greek yoghurt and the dark chocolate chips (and optional nuts, if using) until streaks of yoghurt just disappear and the batter is a rich, dark brown colour with visible chocolate pieces. It should smell intensely chocolatey.

Bake to Perfection: Pour the batter into your prepared baking tray, spreading it evenly with the back of a spoon or spatula. Bake for 25-30 minutes. You’ll know they’re done when the edges look set and a skewer inserted into the centre comes out with moist crumbs, but not wet batter. The top should have a slightly crinkled, shiny crust, and the kitchen will be filled with a wonderful, deep chocolate aroma.

Cool and Slice: Once out of the oven, let the brownies cool completely in the tray on a wire rack. This is crucial for achieving that signature fudgy texture. Trying to slice them too soon will result in crumbly, messy squares. Once cool, use the parchment paper overhang to lift them out, then slice into 12 even squares.