Line a 9x9-inch square pan with two crossing pieces of parchment paper, leaving an overhang for lifting out the bars.
Warm the peanut butter and honey in a saucepan (at least 2 quarts) over medium heat, stirring until combined and smooth.
Fold in the oats right away with a wooden spoon or stiff spatula, stirring until thoroughly coated.
Transfer to the prepared pan and press firmly into an even layer. Cover with plastic wrap and refrigerate for at least 2 hours, or until firm and set.
Lift out using the parchment and cut into 16 bars. Drizzle with extra peanut butter, if desired. Serve at room temperature or enjoy chilled.
Notes
Peanut butter: Use regular creamy peanut butter. Natural peanut butter that separates can change how the bars hold together.Oats: Use old-fashioned rolled oats for the intended chewy texture.Press firmly: Use the flat bottom of a glass or measuring cup to compact the mixture. A 9x9-inch pan makes bars about ½ inch thick; an 8x8-inch pan makes thicker bars.Storage: Keep covered at cool room temperature for up to 4 days or in an airtight container in the refrigerator for up to 7 days. The bars soften in a warm room. Serve at room temperature or chilled.Freezing: Wrap bars individually, place in an airtight freezer container, and freeze for up to 2 months. Thaw overnight in the refrigerator.Nutrition: Estimated per bar, based on 16 bars. Optional extra peanut butter drizzle is not included.