In a heavy-bottomed 2-quart saucepan (choose one with a light-colored bottom to easily monitor the caramel's color), combine sugar and water. Heat over medium-high heat, whisking constantly to ensure the sugar dissolves.
Once the mixture reaches a boil, stop whisking and allow it to boil undisturbed until it transforms into a dark amber color. Carefully swirl the pan occasionally; this process requires patience, as it will take some time. Initially, the mixture will bubble vigorously and appear clear. As it continues to boil, the bubbles will become smaller and slower, and the color will gradually shift from yellow to a medium shade of orange.
As soon as the mixture reaches the desired orange hue, promptly add the butter and whisk until it melts, then remove the saucepan from the heat. Carefully pour in the cream, whisking with a long-handled whisk to combine, as the mixture will bubble vigorously. Continue whisking until the caramel is smooth, then transfer it to a bowl or jar to stop the cooking process.
After 35 minutes of baking, remove the cake from the oven and pierce it all over with a chopstick. Slowly and evenly pour the prepared caramel sauce over the cake, reserving a few tablespoons for drizzling before serving. Sprinkle the top with almonds.
Return the cake to the oven and continue baking until cooked through, about 10 more minutes. Once done, remove the cake from the oven and let it sit for 10 minutes. Run a knife around the edges of the cake to loosen it, then remove the pan ring. Finish by sprinkling with sea salt flakes and serve warm or allow to cool completely before storing in an airtight container.