(Optional but recommended) Wrap the saffron in a small square of aluminum foil, then toast in a hot pan or oven for about 1 minute. Remove from the pan and set aside to cool.

Lightly crush the saffron threads (e.g. with a mortar and pestle) and place into a small container. Pour hot water over the saffron, then loosely cover the liquid and set it aside, ideally for about 4 hours (see note).

Peel the spot prawn tails (take care - they've got some spines) and set the shells aside for making the stock.

In a small saucepan, heat 2 tsp of olive oil over medium-high heat. Add the crushed chilies and allow them to sizzle for about 30 seconds. Add the spot prawn shells and continue to cook for another minute, stirring a little to mix everything together. Add 3/4 cup of water, cover and bring to a boil. Reduce the heat to low and simmer.

Cook the stock for 15 minutes, then remove from heat and cool. Strain the stock to remove the prawn shells and peppers, then set aside.

Add butter and olive oil to a large saucepan or pot on the stovetop. Heat over medium. Once the butter has melted, add the onions and saute for 5-7 minutes, or until the onions are fragrant and somewhat translucent.

Add the garlic and saute for another minute.

Add the diced tomatoes and their tomato juice to the pot. Stir to combine.

Add the saffron water to the pot and bring the mixture to a simmer. Cover the pot and simmer over slightly reduced heat for 20 minutes, stirring occasionally. If the sauce thickens too much or is in danger of scorching, add a little water.

Add the spot prawn stock to the sauce, stir to combine, and simmer for an additional 20 minutes.

Use an immersion blender (or transfer the sauce to a blender/food processor) to blend the sauce to the desired consistency. I like it relatively smooth, but you can leave it chunky/rustic if you prefer.

Salt to taste. If ready to serve, leave the sauce simmering over low heat. If not, remove from heat and return it to a simmer before continuing to the next step.

Bring a large pot of salted water to boil. Cook the pasta until al dente, per the package instructions. Drain the pasta, retaining about 1/4 cup to add to the sauce.

Add the spot prawns and about 1/4 cup of the pasta water to the sauce. Continue to simmer until the prawns are just cooked through (about 3 minutes). Take care not to overcook the prawns, as they will become rubbery.

Plate individual portions of pasta. Top each serving with sauce. Add a large dollop (about 2 tbsp) of mascarpone, then top with 5 prawns and a little chopped parsley. Serve immediately.