How do you bake a birthday cake when living off-the-grid?

I solved it by having his sister who lives elsewhere, bake a cake and bring it over as a birthday gift :)

But is there any other way manually aging up a sim on off-the-grid lots?

Do you have the Dine Out GP? If so, I believe you can get a birthday cake at a restaurant, click on your Sims table and there should be an option to request one. I've never tried it myself, but I've read threads on here of other Simmers who have gotten one that way.

Other than that, the only other way I can think to get one would be to buy one at a Bakery if you have one in your world and the Get to Work EP.

EDIT: Just thought of one more way. Throw a birthday party at another location and hire a caterer. They are supposed to bake a birthday cake for the party. Some Simmers haven't had much luck with that though. You could always bake one yourself there too I suppose. Just make sure there's a stove on the venue lot. :)

Thanks @Karababy52 that's very useful info! Yes, I got Dine out, but those living on off-the-grid lots might not be those families who can afford visiting restaurants. I'll check how much the cake costs though, and whether you need to order from menu before the cake is available. I don't have any community lots with a stove (other than restaurants), or wait, there might be a kitchen at Myshuno Meadows. Any way I could arrange something.

You're welcome! Oh, yes, that's right, there's a kitchen with a stove at the wedding venue in San Myshuno Meadows park. I'm guessing you could just travel there, bake the cake and perhaps bring it home to celebrate if you'd rather not have a full blown party at the venue? Just a thought. :)

You can build a retail store running as a bakery to sell cakes so your sims could stop by to get one if they can’t bake one at home.