Use a 26cm spring-form tin. Grease tin. Preheat oven to 180 degrees C. Place flour, salt, egg yolk, butter and 2 tablespoons water in a bowl. Knead well; gather into a smooth dough. Shape into a ball, wrap in cling wrap and chill for 30 minutes.
Combine sour cream, cream, eggs, 1/2 egg white, Parmesan and nutmeg. Squeeze spinach out well and chop coarsely.
Roll the dough out on a lightly floured work surface to line tin. Prick pastry base with a fork; line with baking paper and dried beans. Bake for 12 minutes. Remove baking paper and beans.
Brush remaining egg white over the pastry base. Spread chopped spinach, onions and garlic over the base. Pour in the cream mixture and sprinkle with flaked almonds. Bake quiche for 30–35 minutes. Serve hot.