That is a great question! We call these ADD-ONS. In order to pledge for and receive additional cutlery sets or for more than one pledge level you can do so by editing your total pledge amount to include the cost of an additional set or an additional pledge level.
For example, if you want to order three sets of Brew Cutlery, the easiest way to do so would be to select the double-set pledge option and then edit your total pledge amount to include the cheapest single-set pledge option. As of right now, this would call for you to select the $36 double-set option and then edit your total pledge amount to include the $20 single-set option, which would bring the total pledge amount to $56.
Even though you originally selected the double-set option, the fact that you pledged a total amount the cost of a double-set AND single-set tells us that you want to receive a total of three-sets.