If the chowder is thinner than you'd like and you want to thicken it up, simply mix 1/4 cup cold water with 2 TBSP corn starch in a cup or small bowl. Whisk until starch is completely dissolved. Bring the chowder to a simmer (not a boil) and slowly add the mixture to the soup while stirring. Stir until the chowder thickens.