Pan-fry the garlic and a pinch of the chilli flakes in a generous glug of olive oil over a medium heat for about 3 minutes until the garlic starts to brown.
Add the chopped tomatoes, capers, caper brine and olives, season to taste with salt and pepper, then simmer for about 10 minutes.
Meanwhile, bring a pan of salted water to the boil and cook the spaghetti until al dente. Use tongs to transfer the spaghetti to the sauce, along with a couple of tablespoons of the cooking water and mix it all together. Sprinkle with the remaining pinch of chilli flakes and drizzle with a glug of olive oil to serve.