Melt 1 cup butter in a skillet over low heat. Add garlic and lemon juice. Poach lobster tails for 7–8 minutes, spooning butter over them.
Remove when opaque and firm. Season and garnish with parsley.
In a saucepan, heat olive oil and 2 tbsp butter. Cook diced onion over medium heat until soft, about 5 minutes.
Add Arborio rice and stir for 2–3 minutes until coated and lightly toasted.
Ladle in warm stock, one cup at a time, stirring until absorbed. Continue for 18–20 minutes until creamy and al dente.
Remove from heat. Stir in Parmesan. Season to taste. Cover for a few minutes.
Spoon risotto onto plates, top with lobster, drizzle garlic butter, and garnish with parsley. Serve hot.