1 celeriac (about 750g/1lb 10oz), peeled and sliced into 4 rounds
1 fennel, finely sliced on a mandoline
2 garlic cloves, crushed
1 lemon, juice only
陆 orange, zest and juice
mayonnaise
salt and freshly ground black pepper
2 tbsp rose harissa
1 tbsp sweet white miso
1 tbsp extra virgin olive oil
1 tbsp pumpkin seeds, toasted
75g/2陆oz unsalted butter, melted
4 burger buns, toasted