In a large bowl, mix together flour, baking powder, and salt.
In a separate bowl, mix together egg yolks, sugar, butter, lemon zest, and milk.
Add the liquid mixture to the dry ingredients and mix to combine.
In a third bowl, beat the egg white until stiff peaks form.
Add the whipped egg white to the mixture.
Gently fold the mixture together to combine. You do not want to deflate the egg whites, you just want them mixed in.
Scoop mixture in to waffle maker and cook per manufacturer's instructions until golden brown.
Remove waffles to a cooling rack and continue cooking additional waffles. You can also place cooked waffles in a 200 degree oven to keep warm.
Serve with syrup.
To make the Blackberry Syrup:
Place blackberries in a a small sauce pan.
Add the sugar, lemon zest and water.
Bring to a boil, then reduce heat and simmer for 25 minutes stirring occasionally.
Remove from heat and mash berries with a potato masher or the back of a wooden spoon.
Pour mixture into a bowl through a fine mesh strainer and push pulp through with a spoon. Allow mixture to sit and continue to drain into the bowl for 30 - 60 minutes.
Serve immediately, or store in the refrigerator until ready to use.
Notes
This recipe makes a thin syrup. If you would prefer a thicker syrup: