Watch the magic pumpkin (soup simmer on your stove)!  These masks won’t make your head or your baking projects explode into snakes, but they may very well be part of a Samhain conspiracy.
Of course since trivets don’t have to fit you have some gauge flexibility, but for a nice squishy, protective finished product measuring approximately 7”x9”, your gauge in double knitting (it’s different, I promise!) should be 4 stitches  and 5.5 rows per inch.
Remember to only use natural fibers when making potholders and trivets, you don’t want them melting with the heat of your cauldron.  For seamless edges in double knitting I recommend Judy’s Magic Cast On and the kitchener stitch for the bind off.