Heavy aluminium baking pan. Model is no longer listed on the manufacturer's site, but the advice for their other current heavy cast aluminium tins should apply https://www.nordicware.com/products/naturals-compact-ovenware-muffin-pan/

Don't put it in the dishwasher - handwash with hot soapy water and non-metal pads/ scourers.
Before use, brush with solid vegetable shortening and dust with flour, or spray with a mix of unsalted vegetable shortening and flour.