Line a baking pan with aluminum foil. If you want thicker bars, use an 8- x 8-inch pan; if you want thinner bars, use a 9- x 13-inch pan.
Melt the chocolate chips in a small pan over low heat, making sure not to burn the chocolate. You can also do this in the microwave: Make sure the bowl you use is microwave-safe, and nuke your chips for 30-second intervals, stirring after each. Again, make sure they don't burn.
When the chocolate is melted and smooth, fold in the Rice Krispies and anything else you want incorporated into the bars. Smooth into the baking sheet and top with flaky sea salt, if using. Freeze until set.
Note: If you want to make these vegan, be sure you're using chocolate without any milk solids in it. Lots of dark chocolate is vegan -- just check the ingredients list!