Preheat your oven to 180°C (350°F) and prepare a baking sheet lined with parchment paper.

Cream together softened butter and brown sugar in a large mixing bowl for 2-3 minutes until light and fluffy. Mix in the egg or flax egg and vanilla until well incorporated.

In a separate bowl, whisk together oats, flour, and sea salt until evenly mixed.

Gradually fold the dry mixture into the wet ingredients until just combined, being careful not to overmix.

Drop dollops of batter onto the lined baking sheet, spacing them about 5 cm (2 inches) apart.

Bake for 10-12 minutes, watching for golden edges and soft centers.

Let cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.