Begin by combining 1¾ cups (225g) bread flour, 1⅔ cups (225g) whole wheat bread flour, 1 tsp salt, 1 tbsp light muscovado sugar, and 1 tsp ground cinnamon in a large mixing bowl.
Create a well in the center and add 3 tbsps (40g) melted salted butter, 1¼ cups (300ml) warm water, and 1 × ¼-ounce (7g) packet fast-acting dried yeast. Mix all ingredients together to form a fairly sticky dough, then knead for 4–5 minutes, adding a little additional flour as needed to reach the desired consistency.
Transfer the dough to an oiled bowl, cover tightly with plastic wrap, and allow it to rise in a warm place for 1–1½ hours until the dough has doubled in size.
Once the dough has risen sufficiently, turn it out onto a lightly floured surface and flatten it slightly. Knead in 1 cup (115g) finely chopped walnuts and ¾ cup (115g) raisins until they are evenly distributed throughout the dough.
Shape the mixture into one long loaf or two smaller loaves and place them on a parchment-lined baking sheet. Cover the sheet loosely inside a large plastic bag and allow the loaves to proof for 35–45 minutes until they have risen again.
Preheat the oven to 425°F while the loaves are proofing. Once proofing is complete, brush the top of each loaf with 1 extra-large egg that has been beaten, which will create a beautiful golden glaze.
Bake for 20–25 minutes until the loaves are golden brown and sound hollow when tapped on the bottom. Remove from the oven and cool on a wire rack before slicing.