The older catalogs typically call those iron heaters. One would remove two stove eyes and the hour glass piece in between and place that pan in the elongated hole. Then the sad irons would be placed on/in it to heat. Man people use these as griddles now, but from what I've seen is the old griddles have a pour spout on them, to pour out any grease, where yours does not, making me want to call it a sad iron heater pan. Many foundries made those and most are unmarked. Maybe some one else can help with the ID.