01 - Preheat oven to 350°F and line a 6-cup muffin tin with paper liners.
02 - Whisk together flour, cocoa powder, baking powder, baking soda, and salt in a medium bowl.
03 - Whisk sugar, egg, milk, oil, vanilla, and lilac syrup in a separate bowl until smooth.
04 - Add dry ingredients to wet ingredients and mix just until combined. Do not overmix.
05 - Gently fold in chocolate chips if using.
06 - Divide batter evenly among liners, filling about 3/4 full.
07 - Bake for 16–18 minutes or until a toothpick inserted into center comes out clean.
08 - Cool in pan for 5 minutes, then transfer to wire rack to cool completely.
09 - Beat butter and powdered sugar until light and fluffy. Mix in lilac syrup until smooth.
10 - Frost cooled cupcakes with lilac buttercream and top with fresh lilac blossoms.