Preheat the oven to 180C / 350F and line a medium-sized loaf tin with parchment paper.
In a large bowl whisk the bananas until soft (this will happen easily), then add the eggs, milk, oil, and sugar. Whisk until well combined.
Sift the flour, baking powder, baking soda and salt into the wet mixture and gently fold until it's incorporated.
Empty this into the lined baking tin and top with the additional sugar, chopped walnuts, and sea salt flakes. Bake for 50 - 60 minutes until golden and baked through. To test if it’s done, insert a sharp knife into the thickest part of the loaf and if it comes out clean it's done. If necessary, loosely cover the loaf with tin foil from about halfway through to prevent over browning.
Allow this to cool in the tin for a while and then remove to cool on a wrack.