I found the recipe for this at the Hollandse Pot website and after a quick translation here is the recipe that I followed:
250g self raising flour
pinch of salt
2 teaspoons speculaas spices - available at the German Christmas market at the mo!
150g golden caster sugar
2 teaspoons milk plus a little for brushing
50g sliced almonds
In a mixer place flour, salt, sugar, spices and butter. Blitz to breadcrumbs and then slowly add the milk as if you were making pastry (I needed a little more than 2 teaspoons in the end). Then I would suggest leaving it to rest in the fridge for 30min or so as I tried to roll it out straight away but it was a bit soft. Roll out the marizpan to about 1 cm in depth and then roll out the dough to twice this size. Place the marizipan inside dough and fold over so that it is totally encased in dough. Stick down the edges with a little milk and brush the top with milk also. Scatter over the sliced almonds and bake in a preheated oven at 150°C for 30 to 40 min. Allow to cool and then enjoy with a cup of tea or mulled wine!