Combine the peanut butter, coconut flour, maple syrup, and salt (if using) in a medium bowl and stir well to combine. The mixture should still have a peanut butter-like texture, but it should be thick enough to easily pinch between your fingers and hold its shape.
Line a baking sheet or plate with parchment paper and place your cookie cutter of choice on top of it. Use your hands to pinch off about a tablespoon of the peanut butter dough and press it into the cookie cutter, using your fingers to press the dough evenly into the shape. Feel free to use more or less batter to create the thickness you want. (This will vary depending on the size of your cookie cutter.) Use your fingers to gently press the dough into the lined baking sheet as you pull the cookie cutter upwards, releasing the dough from the cookie cutter.
Repeat this process with the remaining dough and place the cut-out shapes in the freezer to firm up, about 20 minutes.
To prepare the chocolate coating, melt the dark chocolate chips and coconut oil over a double-boiler. (I just use an oven-safe bowl over a small sauce pot filled with an inch of boiling water.) Remove the heart-shaped peanut butter dough from the freezer and use a spoon to coat the tops and sides of each piece. Note: This can get a little messy!
Place the hearts in the freezer for a few minutes to let the chocolate harden, then remove and coat the bottoms with chocolate if you like, too. Keep the chocolate covered hearts in the freezer until ready to serve-- they will melt quickly at room temperature.
*Most dark chocolate brands I've seen are naturally vegan, but be sure to check the label to ensure they are dairy-free if that is important for you. You can also use my recipe for chocolate bark for a naturally-sweetened chocolate coating. (Use maple syrup for a vegan version.)