Explain a joke without telling the joke first

Although the artisan baker operated an effective monopoly over cake sales in the small High Street, she wielded her economic power responsibly and priced every cake variety in her shop window at a flat rate of £1, thus ensuring that her product remained affordable and attractive to local residents. Unfortunately a rash experimentation with Portuguese baking styles combined with a humorous misunderstanding of the appellation "Madeira cake" resulted in rich fruitcakes being priced at 20% more than this baseline.