apple slab pie: birthday edition

Name: apple slab pie: birthday edition
Prep time: 40 min
Cook time: 50 min
Total time: 1 h 30 min
Cuisine: American
Ingredients: 3 3/4 c (473g) all purpose flour; 1 tbsp granulated sugar; 1/4 tsp kosher salt; 1 1/2 c (3 sticks, 340g) unsalted butter (cold, cubed); 2/3 c rainbow sprinkles; 12-14 tbsp (about 3/4 c) ice water; 8-9 apples (mix of golden delicious, granny smith, honeycrisp, braeburn); 6 tbsp unsalted butter; 1/2 c light brown sugar (packed); 1/3 c granulated sugar; 1 tsp kosher salt; 3 tsp ground cinnamon; 1/4 tsp ground ginger; 1/4 tsp ground nutmeg; 1/4 tsp ground all spice; 3 tbsp corn starch (added after cooking); 1 egg; 1 tbsp milk; 1/4 c granulated sugar (to sprinkle on top); 1 1/2 c powdered sugar; 1-2 tbsp milk; 1 tsp vanilla extract; 2 tbsp non-pareil sprinkles