Put the lemons in a small/medium pot and cover with water. Bring to a boil and then simmer for 30 minutes. Then either drain the water or remove the lemons from the water and let cool. The lemons will be soft and may break open.
Preheat the oven to 350°F, and grease your bundt pan. (See notes for other size pans.)
In a separate bowl, whisk together the all-purpose and almond flours, baking powder, and salt. Make sure the ingredients are combined with no lumps.
When the lemon is cool, cut the lemon in half, and scoop out the seeds, stem, and any fibrous parts of the lemon.
Put the lemon rind, eggs, and sugar in the food processor/blender and blend until smooth.
Pour the blended lemon mixture into the bowl with the dry ingredients. Add the oil and apple sauce.
Using a spatula, fold to combine all ingredients. Pour into prepared pan.
Bake at 350F for 45-50 minutes. Test that the cake is done when a toothpick inserted into the center of the cake comes out clean.
Optional for serving: When the cake is cool, dust with powdered sugar, slice, and serve.