Add the rosemary to a food processor along with the walnuts, salt and pepper. Pulse to combine, forming a crumb.
Melt the butter in a small pan over a gentle heat and add the crumb mixture, stirring well until coated in the butter. Set aside to cool slightly.
Line a large ramekin with plastic wrap, so that it is overhanging the sides. Tip in the crumb mixture. Press down to form a firm and even layer. Transfer this to the fridge to set whilst you prepare the cheese.
Add the cream cheese and blue cheese to a mixing bowl and mash together until thoroughly combined.
Remove the set base from the fridge and spoon over the cheese layer. Return to the fridge for a further 30 minutes to firm up. Carefully lift the cheesecake out of the ramekin using the plastic wrap. Slice to serve.
