Preheat oven to 350°F (175°C). Grease a 9x9-inch metal baking pan and line with parchment paper, leaving an overhang on two sides for easy removal.

In a medium bowl, whisk together brown sugar, flour, cinnamon, and nutmeg. Cut in cold cubed butter with a pastry blender or fingers until coarse, pea-sized crumbs form. Stir in chopped pecans and chill in the refrigerator.

In a separate bowl, toss finely diced apples with 1 tablespoon granulated sugar, 1/2 teaspoon cinnamon, and lemon juice.

In a medium bowl, whisk together flour, baking powder, baking soda, and fine sea salt.

In a large mixing bowl with an electric hand mixer (or stand mixer), beat softened butter and granulated sugar on medium-high speed for 2 to 3 minutes until pale, fluffy, and aerated.

Add eggs one at a time, beating well after each addition. Beat in pure vanilla extract.

With mixer on low speed, alternate adding dry ingredients in two additions with the sour cream and milk, mixing just until combined (do not overmix or cake will become dense).

Spread half of the thick cake batter evenly into the prepared pan using an offset spatula.

Scatter all diced cinnamon apples evenly across the batter layer, followed by half of the chilled streusel topping.

Drop dollops of the remaining cake batter over the apple layer and spread gently. Scatter the remaining streusel generously over the entire top, pressing lightly so it adheres.

Bake at 350°F (175°C) for 42 to 46 minutes until the streusel is crisp and golden brown, and a wooden toothpick inserted into the center comes out with a few moist crumbs (no wet batter).

Cool cake in the pan on a wire rack for 25 minutes.

In a small bowl, whisk powdered sugar, apple cider (or milk), and vanilla until smooth. Drizzle glaze warmly across the top of the cake. Slice into generous bakery squares and serve warm.