Instructions
Load the desired family's household. Click on a Sim to select it. Look in the menu on the bottom of the screen. On the left, players can find a blue icon depicting a skyscraper. Click on the icon to open Map View, which displays the neighborhood.
Move the cursor over buildings in the neighborhood. Click on the Supermarket located in the neighborhood. In Sunset Valley and Riverview, the supermarket is named "Everfresh Delights Supermarket." Select "Shop for Groceries." A list of grocery items appears. Click on "Birthday Inferno Birthday Cake," located at the bottom of the grocery listing. Select the "Purchase" button to buy the cake. The cake now appears in your Sim's inventory.
Select the "Map View" icon again. A green icon depicting a house indicates your Sim's home. Click on that icon to make your Sim go home. In the menu on the bottom of the screen, select the blue arrow icon on the right. This opens up icons for your Sim's Skills, Relationships and other information. Hover the mouse over the "Inventory" icon and select it. Click on the birthday cake and drag it to a counter or table in the Sim's home.
Enter "Buy Mode" for an alternative way to purchase a birthday cake in "The Sims 3." Choose "Sort by Function" and then "Parties." Navigate through items until you find the Birthday Inferno Birthday Cake. Click on it, then place it on a table or counter in your Sim's home.