I'm strongly with the others here who think you're husband likely asked a friend's wife to make the dish because he thought it would hurt your feelings to make a dish for an office that just let you go. Honestly I don't think he did anything wrong being that he did it with the best of intentions. We all have been guilty of that.
Your words may be saying you're past it and that you don't care, but I hear something totally different in your tone. You sound bitter still and you're making comments such as, "She can wash his undies for all I care" and saying she can do lots else for him so you'll have more time for yourself. It's true we have to learn to let lots go for the sake of a happy marriage, but you haven't truly let this go. I highly suggest you tell him how it hurt your feelings, but that you understand why he did it (unless you think he did it for another reason). Tell him next time you'd like to make his contribution to the office parties.
My mom once told me men's thought process was like waffles, whereas women's thoughts were like spaghetti. When you pour syrup on waffles it stays in each compartment. It doesn't flow easily from one area to the next. This is how men think. They are really best at thinking about one thing at a time. They typically aren't very good at thinking all the way through, and thinking about every angle of a situation. When you pour sauce on spaghetti it goes everywhere, all through the noodles. That's how women think. They think from the start to the end and to the right and to the left, and every other angle in between. Neither is better, just different. God blessed each gender with strong points that would compliment the other's weakness.
Talk to your husband and then truly let go. It will do you a world of good.