Preheat oven to 350°F. Grease a 9-inch cake pan, line with parchment paper, and grease the paper; set aside.

Place the sugar and water for the caramel in a small saucepan, and bring to a simmer over medium heat. Continue to cook for about 10-15 minutes, swirling the pan, until the caramel reaches a golden color. Add in the butter and salt and swirl until melted.

Pour the caramel into the cake pan, and place enough tangelo slices in the bottom of the pan to cover.

In the bowl of an electric mixer fitted with the paddle attachment, cream together the sugar, butter, zest, and almond extract for 5 minutes. Add in the flours, baking powder, and salt, and mix on low. Add in the eggs, and mix until just combined. Spread the batter over the tangelos and caramel.

In a small bowl, mix together the cinnamon, sugar, and almonds. Sprinkle over the batter. Cover the cake with a round of parchment paper and bake for 45 minutes. Remove the parchment paper cover and bake for an additional 15 minutes, until cooked through.

Allow the cake to cool for 5-10 minutes, then invert onto a platter.