Shell and devein shrimp, placing shells in saucepan and setting shrimp aside.

Remove stalks from fennel bulb; reserving 3 tbsp/45 mL of the fronds, chop and add to saucepan. Chop bulb; reserving 2 cups/500 mL, add remainder to saucepan.

Thinly slice half of the onion and add to saucepan; chop and reserve remainder.

Add celery, parsley, bay leaf, salt and 6 cups/1.5 L water to saucepan and bring to boil; reduce heat to medium and boil, uncovered, for 10 minutes. Reserving liquid, strain, discarding solids and returning stock to saucepan; bring to gentle simmer and maintain over low heat.

In saucepan, heat oil and butter over medium-high heat; sauté shrimp until pink, about 2 minutes. With slotted spoon, transfer to bowl.

Add garlic and reserved fennel bulb and onion to pot; sauté until light golden, 8 to 10 minutes. Reduce heat to medium. Push vegetables to edge of pan; in centre, fry anchovies, tomato paste and pepper until paste is slightly darkened, about 1 minute.

Add rice and fry until fat is absorbed, 1 to 2 minutes. Add wine; cook, stirring, until evaporated. Add 1 cup/250 mL of the stock; cook, stirring constantly, until liquid is absorbed. Continue adding stock, 1 cup/250 mL at a time and stirring almost constantly, until rice is creamy and tender yet slightly resilient, about 18 minutes in total.

Add shrimp; cook, stirring, until heated and just cooked through, 1 to 2 minutes. Adjust salt to taste.

Chop and stir in reserved fennel fronds with 1/4 cup/60 mL of the stock. Serve immediately.

Makes 4 main-course dinner servings, or 6 first-course or lunch servings.