Preheat oven to 325ºF. Trace the bottom of the springform pan onto parchment paper and cut it out. Line the bottom of a 9-inch springform pan with parchment circle and lightly oil the sides of the pan with a little bit of the butter. Line a baking tray with parchment and place the pan on top: This will make clean up easier.

To make the crust, break the graham crackers into a food processor and blend until finely ground. Add melted butter and pulse until the mixture resembles wet sand. Empty the crumbs into the springform pan and firmly press them evenly into the bottom and up the sides.

To make the filling, place all the ingredients in a high-speed blender. Blend, while scraping down sides occasionally, for about 2 minutes, or until completely smooth and creamy. There should be no gritty texture in the mixture.

To assemble the cake, pour the filling into the springform pan. Set the oven rack in the bottom position. Place springform pan on a baking tray lined with parchment and place in the oven. Bake for about 50 minutes. If you notice the top is browning too much, place a piece of foil over the top of the pan without touching the filling.

To make the salted caramel sauce, place the sugar in a small, heavy-bottomed pot. Heat over medium-high heat, while stirring occasionally. As the sugar heats, it will begin to melt and darken. When that starts to happen, you'll need to stir it more frequently. Once the sugar is completely dissolved, remove the pot from heat and stir in the butter. When the butter is melted, place the pot back on the heat and stir in the milk. Cook, while stirring, until the mixture just starts to bubble. Keep cooking for about a minute after the initial boil then remove from heat. Stir in vanilla and salt and set aside to cool.

The cake is done when it is mostly firm to the touch around the outer perimeter with a slightly less done center. The edges should be light golden brown. It will firm up further when cooled completely. Remove the cake from the oven and let cool on the counter before putting it into the refrigerator to chill for several hours or overnight.

To serve, cut slices and place on plates. Drizzle with salted caramel sauce and sprinkle with flaked salt. Extra caramel sauce can be stored in a sealed container for up to a month.