Preheat your oven to 190C/170C Fan and line a 9x9" square tin with parchment paper.
In a bowl, whisk together your plain flour, bicarbonate, salt, and cornflour. Leave to the side for now.
In a different bowl, melt the butter. Add in the two sugars, and whisk together the mixture for two minutes until the sugar starts to dissolve, and the mixture is smooth.
Add in the egg, and the vanilla, and briefly whisk again until smooth.
Add in mixed dry Ingredients and beat until a thick cookie dough is formed. Once in, add in the chocolate chunks, and the coloured chocolates and make sure its all mixed together evenly.
Press the cookie dough into the bottom of the tin, and bake in the oven for 20-25 minutes. The top of the cookie dough will look dry and baked, and the mixture shouldn't wobble when baked.
Let the mixture cool for about 10 minutes, and then let it cool fully out of the tin on a wire rack. Cut into squares and enjoy!
I found my pink/white/red chocolate sweets in Tiger (Flying Tiger) randomly, but they're heart shaped and perfect! M&Ms or Smarties, or anything similar would also work! Aim for red/pink colours.
These treats will last in an airtight container at room temperature for 4 days.
I used milk and dark chocolate chunks to make these extra chocolate as you can see in the images, but you can use all the coloured ones if you want!
Microwave each piece for 30 seconds, and add a dollop of ice cream for an indulgent dessert!
If you want to make these smaller for 'just two' you can easily half the recipe and use one small egg. Use one of those foil trays you can buy in a supermarket to bake it in!