Whip heavy cream with powdered sugar and vanilla extract in a mixing bowl until soft peaks form, then refrigerate.
Combine granulated sugar, light corn syrup, and water in a medium saucepan over medium heat and stir until sugar dissolves.
Stop stirring and simmer the mixture until it turns a deep amber color, about 8 to 10 minutes.
Carefully add the warmed heavy cream, then butter and salt, stirring until smooth; remove from heat and stir in vanilla extract.
Pour a thin layer of caramel into a parchment-lined square pan and let it set for 5 to 7 minutes.
Pipe or dollop the chilled vanilla cream filling over the slightly set caramel layer.
Pour the remaining caramel over the cream filling layer to cover completely and smooth the top.
Let the layered caramel cool to room temperature or refrigerate to speed up the setting process.
Once fully set, lift the caramel slab from the pan and cut into squares.
Optionally sprinkle with sea salt or dip squares in melted chocolate before serving.