In a medium sauce pan, combine butter, sugar, water, cornstarch, cinnamon, nutmeg and salt together. Melt over medium heat and bring to a boil. Boil 2 minutes, stirring frequently, and then add in apple. Bring back to a boil over medium-high heat and cook for 5 minutes, stirring often. Remove from heat and let cool.
Mix the brown sugar, cinnamon, and butter together and then mix in the flour until thick and crumbly. Set aside.
Preheat oven to 400 degrees F and line two baking sheets with parchment paper.
Unfold one thawed puff pastry sheet at a time and roll out to 10x10 inches. Use a pizza cutter and make 12 even strips. Connect two strips together by overlapping by a half inch and pressing together. Twist the ribbon and then snail it around itself and press the end to the rest of the dough. Place on a parchment lined pan (6 danishes per baking sheet) and press the middle down. Place a spoonful of apple filling in the wells.
Mix the egg and water together in a small dish and brush the pastry with it. Sprinkle the crumb topping over the tops of each danish and then bake for 16-18 minutes until edges are golden. Let cool for 5 minutes and then glaze.
Mix glaze ingredients together and drizzle over the warm apple danish.