Preheat the oven to 180 C (160 C fan). Grease a 2 lb loaf tin with butter.
Mix together the brown sugar and cinnamon and lightly sprinkle over the butter in the tin - you will have some left.
Unwrap the cinnamon rolls from their packaging and lay out on a work surface - you may need to re-distribute the cinnamon filling along the length of the rolls.
Mix the pumpkin puree, remaining cinnamon brown sugar, other spices and vanilla paste together in a medium bowl. Reserve 2 tablespoons of the remaining cinnamon sugar then add the rest to this bowl and mix through. Divide this mixture between the 4 lengths of dough.
Spread the pumpkin filling out over the dough with an angled spatula and place the dough strips on top of each other, so that you are left with a stack of dough.
Slice the dough stack in half and then each half into half again so you are left with 4 stacks of dough. Place the 4 dough stacks into your buttered and sugared loaf tin one next to the other.
Sprinkle the reserved cinnamon sugar over the loaf then place into the preheated oven and cook for 45 minutes, until cooked through and golden.
Remove from the oven brush with the melted butter, then leave to cool in the tin for 30 minutes.
To assemble: To make the icing, whisk the icing sugar with a few drops of very cold water in a bowl, until you have a viscous icing.
Turn the loaf out of the tin, place on serving plate and drizzle over the icing.