Bring a large pan of water to the boil, crumble in the stock cube and stir until dissolved. Add the pasta and cook for 10-12 minutes until al dente.
Meanwhile, bring another large pan of water to the boil, add the broccoli and cook for 4-5 minutes. Drain and cool in a colander under cold running water.
Toast the pumpkin seeds in a dry frying pan over a medium heat for a few minutes, until golden.
Drain the cooked pasta, cool under cold running water, and put into a large bowl. Stir in the pesto and crème fraîche. Toss in the spinach leaves, tomatoes, broccoli and pumpkin seeds then season with freshly ground black pepper.