Heat the oven to 175 C / 350 F. Line two sheet pans with parchment paper.

Combine the sunflower seed butter, tahini, brown sugar, and granulated sugar in a large bowl. Stir until smooth and the sugars are fully incorporated.

Add the egg and vanilla extract. Stir vigorously until the mixture looks glossy and pulls together, about 1 minute.

Add the flour, baking soda, and fine salt. Mix until no dry flour remains - the dough will be thick and slightly sticky.

Cover the bowl and refrigerate for 20 minutes. This helps the dough firm up so the cookies hold their shape.

Scoop the dough into balls of about 30 g each (roughly 1.5 tablespoons) and place them 5 cm apart on the prepared pans.

Press each ball gently with a fork in a crosshatch pattern to flatten to about 1.5 cm thick. Sprinkle a few flakes of sea salt on top of each cookie.

Bake one tray at a time for 10 to 12 minutes, until the edges look set and lightly golden but the centers still appear soft.

Let cookies cool on the pan for 8 minutes before transferring to a wire rack. They firm up considerably as they cool.