This item is a vintage Castalloy Cook-King baking or roasting dish, manufactured in Adelaide, South Australia. 
Brand: Castalloy
Model/Line: Cook-King
Origin: Made in South Australia
Markings: Features the "Cook-King" logo along with "Regd. Design" and dimensions
Material: Made of cast aluminium alloy, it features a distinctive design that is both functional and durable.
Design Features
Self-Basting Dimples: The regular grid of circular indentations on the top creates "basting points" on the inside. As steam rises and condenses on the underside of the lid, these points cause the moisture to drip back down evenly over the food, keeping it moist while roasting or braising.
Venting System: The rectangular sliding mechanism at the bottom of the lid is a steam vent. By sliding it, you can control the amount of steam that escapes, allowing you to regulate the moisture level and pressure inside the pan during cooking.
Fold-Down Handle: The central handle is designed to fold flat, which makes the pan easier to store or stack when not in use
A high-quality example of mid-century industrial design from Adelaide.
 
It measures 28cm x 28cm.  Its sides have a height of 12cm approx.
 
Dimples molded into the lid replenish moisture back to the meat as condensation builds and drips back down while cooking.
 
It has a vent in the lid. It slides freely.
 
It has markings as shown in the photos. I think it would clean up more.