Spread the sugar out onto the bottom of a heavy bottom saucepan.
Pour the water over the sugar and swirl the pan gently to moisten the sugar evenly. Then place the saucepan over medium-high heat and bring the sugar mixture to a boil.
Allow the sugar mixture to cook without stirring (it will bubble vigorously at first) until it turns a deep caramel color, about 6-10 minutes. Then quickly remove the saucepan from the heat and whisk in the cubed butter.
Gradually whisk in the heavy cream and sea salt. Then carefully transfer the caramel sauce to a clean re-sealable container.
Once it has cooled to room temperature, cover and refrigerate it until you’re ready to use it.
The caramel sauce can be stored in your refrigerator for 2-3 weeks (you’ll have leftover caramel sauce after you finish the tart).
To finish the tart, cut the peaches in half and remove and discard the pits.
Then thinly slice the peaches. Arrange the peach slices in a circular pattern on top of the chilled filling, slightly overlapping the slices.
Start on the outside of the tart and make a single row all around. Then fill in the remaining space in the center. The pattern doesn’t have to be perfect!
Re-warm the caramel sauce in your microwave for about 30 seconds.
Then drizzle about 3-4 tablespoons all over the top of the peaches. Use a sharp knife to carefully slice the tart. Serve immediately.
This tart is best enjoyed shortly after the peaches have been added. If you won’t be serving the tart immediately, keep it chilled in your refrigerator until serving time.