Preheat the oven to 400°F.
Mix the flour, baking powder, and salt in a bowl, and set aside.
In a different bowl, mix the butter and sugar until obtaining a paste. Add the egg and whisk until well combined. Add the milk and lemon zest, then blend for 1 minute or until smooth.
Add the dry ingredients and blueberries, and mix until well combined.
Chill the dough for at least one hour, then form big balls with an ice cream scoop, and put them on a previously buttered oven tray. Put 9 cookies per tray, well separated from each other. Bake for 13-15 minutes. Allow to cool for 5 minutes before taking them off the trays.