Vintage Cake Cover

When I picked this cover, I thought it was the top to a cooking pot, but the woman selling it, told me it was a cake cover. I thought is was a pan top, because the knob has a device to open and reveal a tiny round hole. The exterior looks like brushed aluminum, but I think it is stainless steel. Excluding the knob, it is 5 inches in height and the width is 12 inches. There is one shallow dent and some superficial marks to the surface. I need your zip code to calculate the postage.