Dry roast the okara in a frying pan while stirring (aiming for a golden brown color). It's ok if a few burned bits get mixed in, so keep dry roasting over medium heat.
Leave the dry roasted okara to cool down. Bring the butter to room temperature. Preheat the oven to 170°C.
Mix the sugar and butter together in a bowl. Add the egg and continue mixing until it's the consistency of mayonnaise.
Add the dry roasted okara. When it's been incorporated, add the flour in 2 to 3 batches, and knead the dough. (If you put the dough in a clean plastic bag and knead it over the bag, it comes together more easily.)
Roll about 3 mm thick and cut out with cookie cutters. Bake in a 170°C oven for 10 minutes. If the cookies are baking unevenly, turn the baking sheets around and bake for another 5 minutes while keeping an eye on them.
Story Behind this Recipe
I wanted to go on a diet.
These cookies are baked on two levels in an oven that has residual heat. If adding cocoa powder, use 60 to 70 g of sugar. The baking time will vary depending on your oven, so adjust to your taste.