Preheat and Prepare: First, preheat your oven to 180°C (160°C for fan-assisted ovens). Grease a 20cm x 20cm (8x8 inch) square baking tin and line it with baking parchment, leaving a little overhang on two sides. This will act as a sling, making it much easier to lift the bars out later.

Crush the Eggs: Place about two-thirds of your mini eggs into a sealed plastic bag and gently crush them with a rolling pin or the bottom of a heavy glass. You're looking for a mix of coarse chunks and smaller pieces, not a fine powder. Set aside the remaining whole eggs.

Combine Wet Ingredients: In a large mixing bowl, whisk together the vegetable oil, eggs, and vanilla extract until they are well combined.

Add the Dry Ingredients: Tip the entire packet of cake mix powder and the salt into the bowl with the wet ingredients.

Mix the Dough: Using a sturdy wooden spoon or a spatula, mix everything together until a thick, uniform dough forms. It will be quite stiff, almost like a traditional cookie dough. What works best for me is to switch from stirring to more of a folding and pressing motion towards the end.

Fold in the Add-ins: Gently fold the white chocolate chips and the crushed mini eggs into the dough until they are evenly distributed. Be careful not to over-mix at this stage.

Press into the Tin: Transfer the dough to your prepared tin. Use the back of the spoon or your fingertips to press it down into an even layer, making sure it reaches all the corners. If the dough is sticky, slightly dampening your fingers can help.

Add Topping and Bake: Press the reserved whole mini eggs gently onto the surface of the dough. Bake on the middle shelf of your preheated oven for 22-25 minutes.

Check for Doneness: The bars are ready when the edges are a light golden brown and the centre is just set to the touch. It might look slightly underdone, but it will continue to cook and set in the hot tin. This is the secret to a chewy centre.

Cool Completely: Remove the tin from the oven and place it on a wire rack to cool completely. This is the most important step! Do not attempt to slice them while they are still warm, as they will be too soft and will fall apart. Once fully cooled (at least 2 hours), use the parchment paper sling to lift the block out and slice it into 16 squares.