In a stand mixer, cream the butter and 1 cup sugar together, beating until light and fluffy. Beat in the eggs, milk, and vanilla until combined.
Whisk together flour, baking powder, and salt in a separate bowl to combine. Add flour to the mixer in 2 additions. Mix until dough comes away from the sides of the bowl. Form dough into a disk and wrap with plastic wrap. Refrigerate for at least 20 minutes to chill.
Meanwhile make the filling.
For the filling
Combine all of the ingredients in a saucepan. Bring slowly to a boil and stir until the mixture thickens. Simmer for 2 minutes while whisking. Remove from heat, allow to cool for a few minutes, then place a sheet of plastic wrap over the top to keep a skin from forming. Cool filling completely.
For the apples
Quarter 3 apples and add to a bowl. Drizzle with 3 tablespoons melted butter and 2 tablespoons light brown sugar and toss.
Add apple quarters to hot grill and cook just until lightly carmelized, about 3-4 minutes per side. Remove from grill allow to cool briefly then slice.
Lightly flour your workspace and roll out the dough to ¼ inch thick, then carefully place in a deep dish pie pan, trim the edges then crimp. Pour in the cooled filling into the unbaked shell (you might need to whisk again to get rid of any lumps). Sprinkle top evenly with remaining 1/4 cup of sugar before baking.
Bake the pie at 350 degrees for 30-35 minutes, until the crust is golden brown. The custard filling will still be jiggly.
Remove from oven and cool. Once cool, refrigerate until well chilled and filling is set, at least 2-4 hours. Top pie with sliced apples, a big drizzle of honey, and powdered sugar.