Before you begin, make sure you have a clear space in your fridge that's large enough to accommodate a large baking sheet (at least 13 inches wide). It will need to be level and have a couple of inches of clearance. Line the baking sheet with parchment paper.
Stir the water and cornstarch together in a small container or cup. Set it aside for now.
Place the apples, sugar, lemon juice, cinnamon, ginger, nutmeg, cloves, and salt into a medium saucepan and place it over medium heat. Cook the mixture while stirring occasionally, until the apples soften and begin to release their juices, about 5 minutes.
Give the cornstarch mixture a final stir to redistribute any settled cornstarch, then add the mixture to the pot with the apples. Stir everything together and cook the mixture for one to two minutes more, until the liquid thickens. Remove the pot from heat.
Gently fold in the raspberries. Some will break, but try to keep a few intact. Let the mixture cool completely, at least 1 hour (Note 2).
Once the filling has cooled, place your pie crust on a lightly floured surface, then use a rolling pin to roll it out into an approximately 12-inch circle. Carefully transfer the dough to your large baking sheet.
Sprinkle the crust with the panko breadcrumbs, leaving an approximately 2-inch border. Place the filling over the breadcrumbs, lightly piling it up into a dome if needed. Keep that 2-inch border of crust.
Gently fold one section of the dough border over your filling. Next, fold an adjacent section over the filling. Continue working your way around the filling, folding a section at a time. You should have an approximately six inch opening in the middle and about 5 to 7 folds, but don't fuss too much over this — remember, this dessert is rustic.
Brush the crust with the non-dairy milk and optionally sprinkle with coarse sugar.
Place the entire baking sheet into the fridge to chill for 30 minutes.
Preheat the oven to 400°F.
Once the oven has heated up, place the baking sheet inside. Bake the galette for 30 to 35 minutes, until the crust is golden brown.
Place the baking sheet on a cooling rack and let the galette cool completely, at least 2 hours.
Slice, serve, and enjoy!