Preheat oven to 325 degrees F. Grease a glass pie dish (9.5 inches, 24cm) with butter.
Place all the ingredients in the food processor. Process until combined.
Transfer the thick batter to the prepared baking dish. Smooth the top out with a spatula.
Bake until browned and fragrant and a toothpick inserted in the center comes out clean, 30-40 minutes. If you need to bake for longer than that, shield the edges with foil strips.
Cool in pan on a cooling rack 10 minutes, then invert onto a cutting board and back onto the cooling rack.
Let the cake cool 20 more minutes before slicing and serving.
Leftovers keep 4-5 days in the fridge, in an airtight container. Remove them from the fridge 30 minutes before serving.
*A reader has informed me that her cake turned out too dry. Coconut flour is very absorbent and finicky, so sometimes you need to add a bit more liquid. If the batter seems extremely thick, consider adding an extra 1/4 cup coconut milk, or even just water.