Heat the oven to 320 F (160 C). Line the loaf pan completely with parchment, leaving enough overhang to lift out the cake.
Stir the honey, warm water, milk, and oil together until smooth.
Mix the Batter:
Whip the eggs and sugar on high speed for 8 to 10 minutes until pale, very thick, and able to hold a ribbon on the surface.
Sift in the bread flour in three additions, folding gently after each. Fold in the honey mixture just until no streaks remain.
Bake and Rest:
Pour into the pan and run a skewer through the batter once to remove large air pockets. Bake for 50 to 55 minutes until the top is evenly brown and the center reaches about 200 F (93 C).
Cool for 5 minutes, lift out, and peel away the parchment. While slightly warm, wrap tightly. Rest for at least 12 hours before trimming and slicing.
Notes
Bread flour gives castella its characteristic resilient crumb.
Fold slowly from the bottom of the bowl so the dense flour and honey do not settle.