To prepare, position the oven rack in the center, then preheat the oven to 350°F. Next, ensure the 9" round springform pan is lightly greased, floured, and wrapped with aluminum foil up to 1" from the bottom to prevent any dough from leaking during baking.
Combine flour, baking soda, cinnamon, nutmeg, and salt in a medium bowl. Whisk until well blended.
With an electric mixer fitted with the paddle attachment, blend butter, sugar, and vanilla in a large bowl on medium speed for approximately 3 minutes until well combined.
Gradually add the eggs, one at a time, ensuring thorough mixing after each addition. Remember to pause and scrape the bowl and beaters as required.
Start by blending in half of the flour mixture at low speed. Then, incorporate the yogurt, and finally, gently fold in the remaining flour mixture.
Evenly spread half of the batter, roughly 1 lb 2 oz when measured, into the prepared pan for baking.
Distribute half of the streusel mixture evenly across the batter.
Spread the remaining batter evenly over the streusel layer for a consistent texture
Position two apple slices on the cake's top and gently press them in.
Evenly distribute the remaining streusel on the top.
To achieve a perfectly baked cake, bake it for approximately 45-50 minutes, or until the top is golden brown, and a toothpick inserted into the center emerges clean. Afterward, let it cool on a wire rack until it reaches a warm or room temperature.
Take the remaining apple slices, cut them in half, and sauté them in a teaspoon of butter for two minutes. After that, drizzle them with caramel sauce, mix everything thoroughly, and place the mixture in the center of the coffee cake.
Enhance the cake by generously drizzling it with additional caramel sauce.