Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan or two 8-inch round cake pans. If using round pans, line the bottoms with parchment paper.
Step 2: In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, ginger, cloves, and salt. Set aside.
Step 3: In a large bowl, cream together the softened butter and granulated sugar with an electric mixer until light and fluffy. Beat in the eggs one at a time, mixing well after each addition.
Step 4: Stir in the pumpkin puree and vanilla extract until just combined. The mixture may look slightly curdled at this point, which is normal.
Step 5: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined; be careful not to overmix.
Step 6: Pour the batter evenly into your prepared baking pan(s). Bake for 30-40 minutes for round pans, or 35-45 minutes for a 9x13 inch pan, or until a wooden skewer inserted into the center comes out clean. Let the cake cool completely in the pan on a wire rack.
Step 7: To make the caramel sauce, combine sugar and water in a heavy-bottomed saucepan over medium heat. Stir until the sugar dissolves. Once boiling, stop stirring and let it simmer until it turns an amber color (about 8-10 minutes).
Step 8: Remove from heat and carefully whisk in the butter until melted. Gradually whisk in the warm heavy cream (it will bubble up). Stir in vanilla extract and sea salt. Let the caramel cool completely, it will thicken as it cools.
Step 9: To make the crunch topping, in a medium bowl, combine flour, rolled oats, brown sugar, cinnamon, and salt. Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.
Step 10: Spread the crunch topping mixture evenly on a baking sheet. Bake at 350°F (175°C) for 10-12 minutes, or until lightly golden brown and fragrant. Let cool completely.
Step 11: Once the cake is completely cool, if using round pans, level the tops if necessary and stack them. If using a 9x13 pan, you can slice it in half horizontally to create two layers if desired, or keep it as one layer.
Step 12: Spread about half of the cooled caramel sauce over the first cake layer (or the bottom layer of the 9x13 cake). Sprinkle generously with half of the crunch topping. Place the second cake layer (if applicable) on top, and repeat with the remaining caramel sauce and crunch topping. Drizzle any extra caramel on top or serve alongside. Slice and serve!