With the rack in the middle position, preheat the oven to 375°F (190°C). Butter a 9-inch (23 cm) pie dish and sprinkle the bottom with 2 tbsp of the spelt flakes.
In a bowl, combine both flours, the brown sugar, baking powder, salt and baking soda. Add the butter and rub into the flour with your fingertips until it forms pea-sized pieces. Make a well at the centre. Pour in the yogurt and milk. Mix just until the dry ingredients are moistened.
Turn the dough out onto a work surface. With your hands, knead the dough until smooth. Shape into a bread about 9 inches (23 cm) in diameter and place in the prepared pie dish. With the tip of a knife, cut a cross about ½ inch (1 cm) deep over the entire surface of the bread. Brush all over with milk and sprinkle with the remaining spelt flakes.
Bake for 45 minutes or until a toothpick inserted in the centre of the bread comes out clean. Unmould. Let sit for 15 minutes on a wire rack before slicing. Spread with butter and serve alongside soup or stew.