In a medium saucepan, combine granulated sugar and water over medium heat, stirring until sugar dissolves. Allow to boil until golden amber, about 8-10 minutes. Add butter and cream, stirring until smooth. Cool in fridge.

Preheat your oven to 340°F (170°C). Line a 22x22 cm baking pan with parchment paper, leaving some overhanging for easy lifting.

In a large bowl, sift together flour, baking powder, baking soda, sea salt, cinnamon, allspice, and both sugars. Set aside.

In a separate bowl, whisk together oil, eggs, sour cream, and vanilla until blended.

Gently fold the wet mixture into the dry until just combined; then fold in grated apples.

Pour the batter into the prepared pan and smooth the top. Bake for 40-45 minutes or until a toothpick comes out clean. Let cool for 10 minutes, then transfer to a wire rack.

In a large bowl, beat the softened butter with an electric mixer until fluffy, about 3-5 minutes. Gradually add sifted sugar and cooled caramel, mixing until creamy.

Once the cake cools completely, spread a generous layer of caramel buttercream over the top. Drizzle additional caramel and garnish with flaky sea salt.