Although they split up years ago, she is still close to the music mogul and gets to share the indulgent puddings with him when they holiday together.
The 43-year-old star says 'The X Factor' boss, 52, insists on being served school dinner-type desserts wherever he is in the world.
She recently went on a Mediterranean cruise aboard Simon's yacht, and admits he rejects expensive gourmet food.
She told the Daily Star newspaper: ''Simon likes nursery nosh, things like rhubarb crumble, sticky toffee pudding and spotted dick.''
She said they both watch their figures but the calorie-packed treats were a guilty pleasure.
The 'So Macho' singer said: ''I'm very careful about my diet and so is Simon, but he always brings his own chef plus the necessary ingredients on holiday and we all just stuff ourselves silly.''
Sinitta, who has acted as Simon's assistant during the Boot Camp stages of 'The X Factor' in the United Kingdom, began dating him in the 1980s when she was a teenager.