Butter and line a 8" / 20cm square dish or pan with baking paper.
Place the Base ingredients in a bowl and mix until combined. Press into the prepared pan.
Melt the Topping ingredients (I do it in the microwave in 2 x 30 second bursts). Pour and spread over the Base - smooth the top or do swirls (see photos for examples of each).
Refrigerate until set - about 1 1/2 hours. Remove from fridge, allow to come to room temp slightly (so top cuts neatly). Cut into 16 squares (or whatever shape you want!). Best served at room temperature.
* Originally published June 2015, updated with new photos, words and recipe video. No change to recipe.1. Biscuits - If you are in the UK, Digestives are great for this recipe. Otherwise, any other plain sweet crisp biscuit (i.e. not a soft biscuit with filling) should work fine - the base has peanut butter as the glue so it's a more flexible recipe than, for example, cheesecake bases.You could even try biscuits like oatmeal or chocolate chip biscuits! To make the crumbs, you can use a food processor or pop them in a ziplock bag and use a rolling pin or can to bash them. Very therapeutic!2. Chocolate - Make sure you use chocolate for cooking/baking, not the eating kind! And if your store sells many types of chocolate chips, get the MELTING chocolate chips (as opposed to the ones that hold their shape in cookies / muffins etc) as they melt easier and smoother. This can be made with milk or dark chocolate. I use dark - not the expensive kind with a high cocoa %, just normal dark chocolate chips.3. Storage - keeps very well, around 5 days in an airtight container. If it's super hot where you are, fridge is best but serve at room temperature.4. Gluten Free option: A reader reported that she used 1 1/2 cups of gluten free pretzels for the base and it worked out great! And a friend of mine has made this with gluten free plain sweet biscuits purchased from the supermarket and said she couldn't tell the difference in the taste or texture.5. Nutrition per serving (assuming 16 slices).