Preheat the oven to 425 degrees Fahrenheit (215 °C). Line a muffin pan or grease well.
Place washed kale, eggs, banana, milk, olive oil, honey, lemon juice, and hemp hearts, if using, into the blender. Blend until smooth, about 1 minute, until there are no kale pieces and everything is liquidy.
Add the flour on top of the 'green smoothie' mixture, then place the baking soda, baking powder, and sea salt on top of the flour. Blend on low speed for 10-15 seconds until fully incorporated.
Pour the muffin batter into the muffin pan, filling each muffin cup full.
Bake for 8 minutes at 425°F (215°C), then turn the oven down to 375°F (190 C) and bake for another 6-7 minutes until they are not gooey inside and they will spring back slightly from touch.