ASPARAGUS, CHEESE & PUMPKIN SEED TART

• 320g sheet ready-rolled puff pastry • 3 tbsp crème fraîche • 1 tbsp Dijon mustard • 1 large egg, beaten • 40g Gruyère, grated • 40g pecorino, finely grated • 2 x 230g packs asparagus • 1 unwaxed lemon, zest • 1 tbsp olive oil • 15g pumpkin seeds