Line an 8x8 inch pan with parchment; lightly grease with butter or cooking spray.
Warm cream and butter in a small saucepan over low until butter melts; off heat, stir in vanilla and 1 teaspoon sea salt and set aside.
Combine sugar, corn syrup, and water in a medium heavy-bottomed saucepan; cook over medium-high, stirring until sugar dissolves.
When boiling, stop stirring and attach a candy thermometer; cook 15-20 minutes until 350°F.
Off heat, carefully add cream mixture; it bubbles vigorously. Stir gently to combine.
Return to medium heat; cook 5-8 minutes, stirring occasionally, until 248°F (firm ball).
Immediately pour into pan without scraping saucepan bottom; cool 5 minutes and sprinkle with flaky salt.
Cool completely at room temperature 3-4 hours or overnight.
Remove from pan; cut into 1-inch squares with a sharp knife and wrap individually in wax paper.
Store wrapped caramels airtight at room temperature up to 3 weeks.