Preheat oven to 350°F. Line a square glass baking dish with parchment paper or lightly grease with oil.

Streusel Topping: Combine flour, brown sugar, granulated sugar, cinnamon, and salt in a bowl. Add melted butter and stir with a fork until crumbly. Set aside.

Cake Batter: Cream together butter, granulated sugar, and brown sugar until light and fluffy. Add eggs one at a time, mixing well after each addition. Mix in Greek yogurt and vanilla until combined. In a separate bowl, whisk together flour, salt, cinnamon, baking powder, and baking soda. Gradually mix the dry ingredients into the wet ingredients until just combined.

Spread half of the batter into the prepared baking dish. Add half of the streusel topping over the apples and spread evenly using a fork. Add the remaining batter and gently spread it over the first layer. Top with the remaining streusel topping.

Bake for 40-45 minutes or until a toothpick inserted into the center comes out clean.

Maple Cream Sauce: Heat the maple syrup in a saucepan over medium heat, allowing it to warm up without boiling.

Add the butter and stir until melted and combined.

Slowly pour in the cream, whisking to incorporate.

Let it simmer on low heat for a few minutes, allowing it to thicken slightly while stirring occasionally.

Add vanilla and a pinch of salt, then remove from heat. Let it cool slightly to thicken more before serving.