Prepare the loaf pan by greasing it with melted unsalted butter and lining it with parchment paper.

Melt ½ cup of unsalted butter and 1 cup of heavy whipping cream in a saucepan over low heat, then mix in a pinch of salt and 1 teaspoon of vanilla extract.

In another saucepan, heat 1 cup of granulated sugar over medium heat, stirring continuously until it melts and turns golden amber.

Remove from heat and slowly drizzle in the melted butter and cream mixture along with 1 tablespoon of lemon juice, stirring to blend.

Return to heat and cook while stirring until the mixture reaches 250°F on a candy thermometer.

Pour the caramel into the prepared loaf pan and cool at room temperature for about 3 hours.

Lift the caramel out using the parchment paper, cut into pieces, and sprinkle with flaky sea salt if desired.