Preheat oven to 375 degrees. Butter and flour a 9-inch springform pan, set aside.

In a large mixing bowl, whisk together flour, baking powder, salt, ginger, nutmeg, and allspice for 20 seconds. Add butter pieces and rub into mixture using fingertips until it resembles fine crumbs. Stir in 1 cup sugar.

Peel apples, slice in half, core and stem, then slice downward into pieces slightly less than 1/4-inch thick, then dice those pieces into smaller chunks. Add apples to flour mixture and toss well to coat.

In a separate mixing bowl, whisk together milk, eggs, and vanilla until well combined. Pour milk mixture over apple/flour mixture and toss just until combined.

Pour batter into prepared baking dish and spread into an even layer. In a small bowl, stir together remaining 2 Tbsp sugar plus 1/2 tsp cinnamon, and sprinkle evenly over cake.

Bake in preheated oven for 45 - 50 minutes until a toothpick inserted into the center comes out clean. Cool about 5 minutes on a wire rack, then remove ring from springform pan and allow cake to cool to desired temperature.

Serve warm drizzled with warm custard sauce or cool with cold custard sauce, as preferred.

For the custard sauce, heat milk with a pinch of salt over medium heat until just boiling.

In a medium mixing bowl, whisk egg yolks and sugar until pale and fluffy.

Reduce heat to medium-low, and while whisking egg yolk mixture, slowly pour in 1/2 cup hot milk mixture. While whisking, pour egg yolk mixture into saucepan. Cook, whisking constantly, until thickened, about 3 - 4 minutes.

Immediately pour into a glass container, stir in vanilla, whisk to cool slightly, then cover with plastic wrap pressing against surface to prevent a skin from forming. Serve warm or cold.