Lightly butter a 9x9 pan or line with parchment paper.
Add butter to a large saucepan over low heat and let it melt.
Add Peeps to the butter. If you're using different colored Peeps, keep them separated in the saucepan.
Let Peeps melt. You can gently stir them a little bit with a wooden spoon, but try to keep each color separate from each other.
Once mostly melted, add Rice Krispies and salt (if using) to saucepan and gently stir together until just combined with colors swirled together.
Press Rice Krispies mixture into the bottom of your prepared pan. Top with additional Peeps if desired.
Let Peeps Rice Krispies treats cool at room temperature for at least 30 minutes before slicing.
Store the cooled Rice Krispies treats in an airtight container at room temperature for about a week.