Maple Walnut Oat Porridge Sandwich Loaf

Steps

1. Make the porridge first: put the oats in a large bowl, pour the boiling water over them, stir and let stand about 20 minutes until lukewarm and thick.
2. While the oats cool, toast the walnuts in a dry skillet over medium heat for 4 to 5 minutes until fragrant, then cool and chop.
3. Beat the egg in a small cup. Set aside one quarter of it, covered, in the fridge for the crust; the remaining three quarters go into the dough.
4. Stir the lukewarm milk, maple syrup and the three-quarters portion of beaten egg into the cooled oat porridge.
5. Add the bread flour, instant yeast and salt, and mix into a shaggy dough. The dough is about 71% hydration (counting the milk's water) and 2% salt.
6. Knead for 5 minutes, then work in the softened butter and knead 5 to 7 minutes more until smooth and elastic. Knead in the walnuts until evenly spread.
7. Cover and let rise at about 75°F (24°C) for 75 to 90 minutes, until doubled in size.
8. Butter a 9x5-inch loaf pan. Press the dough into a rectangle, roll it up tightly from the short side, pinch the seam and set it seam-side down in the pan.
9. Cover and proof at about 75°F (24°C) for 45 to 60 minutes, until the dough crowns about 1 inch above the rim and springs back slowly when poked. Preheat the oven to 375°F (190°C) during the last 20 minutes.
10. Brush the top with the reserved quarter of beaten egg for a golden, glossy crust.
11. Bake 35 to 40 minutes, tenting with foil after 20 minutes if browning fast, until the center reaches 190°F (88°C).
12. Turn the loaf out and cool completely on a rack, about 1 hour, before slicing into 12 slices.