Vegetarian wellington

Name: Vegetarian wellington
Ingredients: 500g butternut squash peeled and cut into 1cm dice; 2 tbsp olive oil; small bunch sage leaves finely chopped; 2 shallots finely chopped; 500g closed cup mushrooms chopped; 3 garlic cloves crushed; 150ml double cream; 200g fresh breadcrumbs; ½ tsp ground mace; 150g cooked chestnuts chopped; whole nutmeg for grating; 500g block puff pastry; plain flour to dust; 6-8 cooked beetroot (similar sized- about 400g); 1 egg beaten, to glaze; 1 tbsp sesame seeds or poppy seeds, to decorate