Line a loaf tin with parchment paper and set aside.
Add the peanut butter, maple syrup, milk, melted coconut oil, vanilla, and salt to a mixing bowl. Whisk to combine. The mixture should thicken slightly when mixed.
200 grams natural peanut butter, 50 ml maple syrup, 1 tablespoon non-dairy milk, 3 tablespoons coconut oil, 1 teaspoon vanilla extract, ½ teaspoon sea salt
Crush the cookies into fine crumbs with a food processor (or a rolling pin between two sheets of parchment paper). Add to the peanut butter mixture and stir to incorporate. Make sure the cookie crumbs are evenly distributed.
150 grams digestive biscuits or graham crackers
Transfer the peanut butter mixture to the prepared loaf tin. Use the back of a spoon or a spatula to press into an even layer.
Chill until set. Freeze for 30 minutes or refrigerate for 4 hours, until the mixture has hardened fully.
Make the chocolate topping. Add the chopped chocolate, peanut butter, and coconut oil to a heat-proof bowl and set over a small saucepan of simmering water (don't let the bottom of the bowl touch the water). This is a bain-marie. Melt the chocolate, stirring occasionally as needed.
Pour the melted chocolate mixture over the chilled peanut butter mixture and tilt the loaf tin to spread the chocolate in an even layer. Chill for another 20 minutes to set.
To slice the bars, turn it out onto a cutting board - line with a piece of parchment paper to reduce mess - so that the chocolate is facing down. Use a sharp knife to slice into eight small squares.
Keep the bars in a sealed container in the refrigerator and serve chilled.
Notes
* You'll need to adjust the amount of added salt to your preference, and also depending on whether salt is added to the peanut butter used. I use salted peanut butter.I didn't measure the ingredients in cups when testing and will have to check what 150 grams of digestive biscuits equals. This will be updated in future but I do always recommend using gram measurements anyway!Storage: keep the sliced bars in a sealed container in the refrigerator for up to one week. Freeze for up to three months.