Mash and strain the blackberries until you have 1 cup juice.
Place strained juice into a small saucepan along with the sugar and 1 teaspoon cornstarch.
Bring the mixture to a slow boil, stirring occasionally. Allow to simmer for one minute, then remove from heat and set aside to cool and thicken.
While sauce thickens, mix the flour, baking powder, and salt together in a large bowl.
In a separate bowl, whisk together the yogurt, milk, eggs, and vanilla.
Add wet ingredients to the dry and stir just until combined. Fold in lemon zest. (Add a bit more milk as needed; batter will thicken as it sits.)
Spray a large skillet or griddle with cooking spray and heat over medium heat.
Drop batter by 1/4-cup fulls onto the hot skillet, then add a few remaining blackberries (if available) to each pancake.
Cook until bubbles appear and the edges seem dry, then flip and continue to cook until golden. Repeat until all batter has been used.
Top pancakes with syrup and any remaining berries. Enjoy!