In a large bowl, combine the cold cubed butter and dry cookie mix. Use a pastry cutter or your hands to mix the butter into the dry ingredients until the mixture resembles coarse crumbs. Finely chop with a knife, or pour slivered almonds into a blender and pulse until the almonds become small crumbs. Pour almonds into butter and sugar cookie mixture.
Add the ice water and mix until a dough forms. Shape dough into a flat disc, wrap in plastic and freeze 10 minutes or until firm.
Preheat oven to 400 degrees and line a cookie sheet with parchment paper. Cut 3/4 of the cherries in half, leaving some whole. If using frozen cherries, defrost cherries before using. Place cherries in a large bowl with the cane sugar, almond extract and salt. Set aside.
Remove dough from freezer and unwrap plastic. Generously flour a flat surface and roll out dough to approximately a 12" circle. Carefully transfer onto the prepared pan. Pile the cherry mixture into the middle of the dough, leaving 2'' of uncovered dough around the circle.
Fold the border of the dough towards the center, pleating the dough slightly. Mix the egg and water together and brush it onto the edges of the dough. Sprinkle with sugar, if desired.
Bake galette for 35-40 minutes until the edges are golden brown. Cool on cookie sheet 10 minutes, then transfer to a wire rack to cool completely. Serve each wedge with a dollop of whipped cream or a scoop of ice cream.