Preheat the oven to 350 degrees F and line an 8-inch springform pan with parchment paper.
Add all of the ingredients for the cake to a blender and blend until completely smooth (note: you can perform this in a mixing bowl using a hand mixer if you prefer).
Transfer the cake batter to the lined cake pan and smooth it into an even layer.
Bake for 35 to 45 minutes, or until the cake has set up and is golden-brown around the edges.
Allow the cake to cool for at least 20 minutes, then release it from the mold.
If desired, sprinkle the cake with powdered sugar and decorate with sliced lemons and fresh rosemary.
Slice and enjoy!
Notes
*If you'd like bigger, bolder rosemary flavor, use 1 Tbsp of dried rosemary. The recipe as written has a light but noticeable rosemary flavor, but it isn't overwhelming.