Butternut squash muffins with a frosty top

INGREDIENTS

• 400 g butternut squash, skin on, deseeded and roughly chopped
• 350 g light soft brown sugar
• 4 large free-range eggs
• sea salt
• 300 g plain flour, unsifted
• 2 heaped tablespoons baking powder
• 1 handful walnuts
• 1 teaspoon ground cinnamon
• 175 ml extra virgin olive oil
• zest of 1 clementine
• zest of 1 lemon and juice of ½ a lemon 1 lemon
• 140 ml soured cream
• 2 heaped tablespoons icing sugar, sifted
• lavender flowers or rose petals, optional
• 1 vanilla pod, split lengthways and seeds scraped out