Cut parchment paper into strips, wrap around the sides of each ramekin, and grease with butter.

Combine sugar and water in a saucepan, stirring over medium heat until the syrup reaches 238°F (115°C).

Whip egg whites in a clean bowl until soft peaks form, then slowly drizzle in sugar syrup while continuing to whip until glossy.

In another bowl, whip heavy cream until soft peaks form, then add vanilla extract and lime zest.

Gently fold whipped cream into the meringue until fully incorporated.

Spoon the mixture into prepared ramekins, cover with plastic wrap, and freeze for 8 hours or overnight.

Before serving, let the soufflés sit at room temperature for 2 minutes to soften, then garnish with lime zest.