Set the oven to 180 °C, or 160 °C fan, and lightly grease an 8 x 8 inch square pan before lining it with baking paper, also called parchment paper. Fit the paper against the bottom and sides so it supports the batter and helps release the cooled bake.

Warm the cubed butter with both sugars in a medium saucepan over low heat, stirring occasionally, then take the pan off the burner once the butter has melted completely. The mixture should look thick and glossy, with no solid butter pieces remaining.

Beat the eggs, salt, and vanilla together in a jug or mug, then stir them into the butter mixture until evenly incorporated. A uniform mixture without separate streaks of egg is the cue to move on.

Use a spatula or wooden spoon to incorporate the flour until smooth, fold through the chopped white chocolate, transfer the batter to the lined pan, and bake for 20 minutes. Stop mixing once no dry flour remains so the thick batter does not receive prolonged beating.

Take the pan out at the 20-minute mark, distribute the mini chocolate eggs over the surface, press them in gently, and bake for another 15 to 18 minutes. Look for a pale golden surface and edges, with the candy resting in the partially set topping rather than buried beneath it.

Leave the baked slab in its pan to cool for at least 1 to 2 hours, or overnight, before cutting it into 9 squares. The center becomes easier to slice as the butter and chocolate firm up, so wait longer if it still feels too soft to hold its shape.