Happiness is your wee boy's face upon seeing his birthday cake that you spent till 4am decorating.
A fudge brownie base, with a devil's food top, a black marzipan road going uphill to a victoria sponge house with a Nice biscuit roof, doors, windows in a green garden complete with paving stones and wee people and a couple of cars (automatic of course). On the bottom level was a white marzipan electrical substation with Electricity. Danger of Death signs, black liquorice laces (power cables) running up to the house attached to cinnamon stick poles complete with triangle electric warning signs. He was amazed. The look and excitement on his face will stay with me forever.
Incidently, he is so into warning signs, danger, electricity etc that it was in his playgroup report. He knows what all the signs are and takes great pains in pointing them ALL out. If you spoke to him, you would assume his daddy was an electrical HSE inspector, which I am not.
But I think I need to plan ahead for next year. I do a theme cake for my kids every year based upon what they are into at the time.