In a medium saucepan, combine the butter, honey, and peanut butter over medium heat. Stir constantly until the mixture is fully melted and just starts to bubble. Let it simmer for exactly 1 minute to develop a slight caramel flavor.

Remove from heat and immediately stir in the vanilla extract, cinnamon, and a pinch of salt.

Add the quick oats to the saucepan. Stir until every oat is coated in the warm peanut butter mixture. The residual heat "blooms" the oats, giving them a slightly toasted flavor without needing an oven.

Line an 8x8 inch square pan with parchment paper, leaving an overhang on the sides. Firmly press the oat mixture into the bottom of the pan. Use the bottom of a measuring cup to pack it down—a tighter pack ensures the bars won't crumble when cut.

In a microwave-safe bowl, combine the dark chocolate chips and the 2 tablespoons of peanut butter. Heat in 30-second intervals, stirring in between, until completely smooth.

Pour the melted chocolate over the oat base and spread it to the edges with a spatula.

Let the bars sit at room temperature for 10 minutes, then sprinkle the flaky sea salt over the top. Adding the salt while the chocolate is slightly set prevents it from sinking.

Refrigerate for at least 2 hours before using the parchment paper overhang to lift the entire block out of the pan. Slice into squares using a warm knife.