Preheat the oven to 180C°, 350F°, Gas 4. Cover a 4x8 loaf tin with parchment paper.
Using a large bowl, mashed the bananas with a fork and add the melted butter.
Then stir in the sugar, beaten eggs, and vanilla extract and add them into the mashed bananas and butter mix.
Add the salt and baking soda to the flour, then add these into the wet mixture.
Add the amaranth and mix well and pour the batter into the loaf tin.
Place in the oven and bake for 40 minutes. To make sure it is properly cooked, insert a toothpick right in the centre, if it comes out wet, let the loaf for 5 more minutes in the oven.
If it comes out dry, let it cool down for a few minutes, before transfer it to a cooling rack.
Once cool down, enjoy it with a hot Mexican chocolote or some tres leches ice cream.