Preheat the oven to 350°F. Grease two 8” round cake pans; line with parchment, and grease the parchment., To make the cake: In a large bowl, whisk together the sugar, flour, salt, baking powder, baking soda, and pumpkin pie spice., In a separate medium-sized bowl, whisk together the eggs, buttermilk, pumpkin, oil, vanilla, and water., Add the wet ingredients to the dry ingredients, stirring to combine. Pour the batter into the cake pans., Bake the cakes for about 35 to 38 minutes, until a toothpick inserted into the center of one comes out clean., Remove the cakes from the oven and let them cool in the pans for 10 minutes. Turn them out onto a rack to cool completely., To make the frosting: Using an electric or stand mixer, beat together the butter and cream cheese at medium-low speed until smooth., Gradually add the confectioners' sugar, beating to combine., Beat in the extracts and salt., To assemble the cake: When the layers are completely cool, level their tops (either both layers, or just the bottom layer)., Place the bottom layer on a serving plate. Frost it, then add the top layer. Frost all over with an offset spatula., If you’re garnishing with the caramel, freeze the cake until the frosting is solid and cold., About 2 hours before serving, melt the caramel on the stove or in the microwave, and stir it for a bit to cool it slightly; you want it pourable, but not so hot that it'll melt the frosting., Pour the caramel over the cake; it should ooze very slowly down the sides of the cake, taking about 90 minutes to do so. Serve the cake within an hour or so after that; letting it sit any longer causes the caramel to begin to puddle at the base of the cake., Garnish with coarse sea salt, just before serving., Store any leftover cake, well-wrapped, in the refrigerator for a day or so; freeze for longer storage.