Preheat the oven to 350°F. Butter a cookie sheet and set aside.
Place almonds in a large non-stick skillet over medium heat, stirring frequently until golden, 3 to 5 minutes. Transfer to the bowl of a food processor and pulse until chopped fine; set aside.
Heat 1 tbsp. butter in the same skillet over medium-high heat until hot. Add onions and sauté until the onions are soft and golden but not caramelized, about 5 minutes.
Place chicken, almonds and onion in a large mixing bowl. Stir in spices, salt, parsley and egg to combine.
Melt the remaining 2 tbsp. of butter. Brush one phyllo sheet with butter on one side. Drape the phyllo over the inside of a small mixing bowl. Press to line the bowl. Repeat with the remaining phyllo sheets, overlapping the sheets slightly as you go so that the corners lie all around the edge of the bowl. (The bowl should be just big enough to hold your filling).
Place the chicken mixture into the center of the phyllo-lined bowl and fold the corners of the dough around the top of the filling to fully enclose it. Brush the top of the pastry with butter.
Invert the bowl onto the prepared cookie sheet and remove the bowl. The basteeya will look like a dome. Brush with any remaining melted butter.
Bake for 25 minutes or until the dough is golden and the filling has heated to at least 165°F. Remove from the oven and place the basteeya on a paper towel using a spatula, to soak up any excess butter. Transfer onto a serving dish and dust with confectioner's sugar. The sugar will melt into the meat as you cut into it and combine with the savory meat filling.