1-Prepare the muffin tin: Prepare the muffin tin: Line a standard 12-cup muffin tin with paper or silicone liners and set aside.
2-Mix the base layer: Mix the base layer: In a medium bowl, stir together the peanut butter, maple syrup, melted coconut oil, vanilla extract, and a pinch of salt until smooth. Add the oats and mix until evenly coated and sticky.
3-Form the cups: Form the cups: Scoop about 2 tablespoons of the oat mixture into each liner. Use the back of a spoon to press the mixture firmly and evenly into the bottom. Transfer the tin to the freezer to chill while you make the topping.
4-Make the chocolate topping: Make the chocolate topping: In a microwave-safe bowl, combine the chocolate chips and coconut oil. Heat in 30-second intervals, stirring between each, until melted and smooth. Alternatively, melt the mixture using a double boiler.
5-Top the cups: Top the cups: Remove the chilled oat cups from the freezer. Spoon about 1 tablespoon of the melted chocolate over each one, spreading it evenly to cover the surface.
6-Add salt and chill: Add salt and chill: If using, sprinkle a small pinch of flaky sea salt on top of each cup. Return the muffin tin to the freezer for 15 to 20 minutes, or until the chocolate is fully set.