Cook spaghetti according to package directions
Caramelize the fennel bulb and onion in olive oil
Add garlic, anchovy fillets, capers, and fennel seeds
Toss cooked spaghetti with the caramelized fennel and onion mixture
Add spaghetti cooking water as needed to create a sauce
Finish with fresh dill and fennel fronds
Season with salt and freshly ground black pepper
Top with Parmesan if desired