Preheat the oven to 180°C/350°F/Gas 4.
To make the cookies, in a large bowl, cream together the butter and brown sugar for 1-2 minutes until well combined.
Next, add the ground flax mixture and vanilla extract and stir, then add the flour, oats and chocolate chips, mix into a dough and leave to chill in the fridge for 20 minutes.
Line a baking tray with parchment paper and roll three tablespoons of cookie dough into a ball, place on the tray and flatten slightly, repeat this with all of the mixture. Be sure to leave room around each cookie, as they will spread once cooking.
Place into the oven for 15 minutes. The cookies should start to set and brown on the edges but still be soft. Remove from oven and leave the cookies for 10 minutes to cool a little. At this point, just before they have hardened and are still a little soft, slice them straight through the middle to make two halves.
Once cooled completely, spread the jam or sauce over the flat side of each cookie half. Then, on one half, stick the marshmallows in a row, like teeth, to the jam. Sandwich another cookie half on top of the row of teeth. In between the two front marshmallows, slide an almond slice as fangs. Repeat with all cookies.
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