Line a 20 x 20 cm (8 x 8-inch) baking pan with parchment paper.

In a large mixing bowl, stir together the peanut butter and honey until smooth.

Add the oat flour, chocolate protein powder, cocoa powder, and salt. Mix until combined.

Add ¼ cup of milk and continue mixing. Gradually add more milk, one tablespoon at a time, until the mixture holds together easily when pressed. I used about 8 tablespoons (½ cup), but this may vary depending on your protein powder.

Transfer the mixture to the prepared pan and press it firmly into an even layer.

Melt the dark chocolate and peanut butter together in the microwave in 20-second intervals, stirring between each, or over a double boiler until smooth.

Pour the melted chocolate over the protein bar base and spread evenly. Sprinkle with flaky sea salt if using.

Refrigerate for 1–2 hours, or until the chocolate has completely set.

Remove from the refrigerator and let the bars sit at room temperature for about 10 minutes before slicing. Use a warm, sharp knife, wiping it clean between each cut for the neatest slices.