Combine the ground flax and hot water. Whisk, quickly, until the seeds have formed a thick, viscous slurry. Set aside to cool.
Whisk together the yeast, sugar, and heated milk. Set aside until mixture has doubled in volume, about 20 minutes.
Combine flour and starches in a bowl of a stand mixer (or a large bowl); whisk gently to incorporate air. Add powdered milk, sugar, pectin, ground cinnamon and salt; whisk to combine well. (If using stand mixer, stir on low to prevent dusting your kitchen with flours.) Cut in butter with a pastry cutter or two knives until mixture resembles coarse meal.
Combine eggs, egg yolk and vanilla in a small bowl with a wire whisk. Add egg mixture to flour mixture; add flax slurry and yeast mixture. Mix well for 5 minutes. Stir in currants and orange peel.
Scrape dough into a bowl coated with cooking spray and let rise in a warm place for 90 minutes or until doubled in size. Lightly spray muffin tin (or paper baking cups) with cooking spray. Scoop dough with an ice cream scoop into muffin tin (or baking cups on a baking sheet) until half filled. Cover with plastic wrap and let rise in a warm place for 20 minutes.
Preheat oven to 375`. Combine egg and water; brush dough with egg mixture. Bake at 375` for 12-15 minutes or until golden brown. Allow to cool.
Combine powdered sugar, milk and vanilla. Drizzle icing over buns in the shape of a cross.