01 - Preheat oven to 350°F. Line a 12-cup muffin tin with cupcake liners.
02 - Whisk together flour, baking powder, and salt in a medium bowl until thoroughly blended.
03 - Beat butter and sugar in a large bowl until light and fluffy, approximately 3-4 minutes.
04 - Beat in eggs one at a time, ensuring each is fully incorporated. Stir in vanilla extract.
05 - Combine elderflower cordial and milk in a small bowl or measuring cup.
06 - Add flour mixture to butter mixture in three additions, alternating with milk mixture. Begin and end with flour. Mix until just combined.
07 - Divide batter evenly among cupcake liners, filling each two-thirds full.
08 - Bake 18-20 minutes until a toothpick inserted in the center comes out clean.
09 - Combine cordial, water, and sugar in a small saucepan. Heat gently, stirring until sugar dissolves. Remove from heat and cool.
10 - Cool cupcakes in pan 5 minutes, then transfer to wire rack. Brush warm cupcakes with elderflower syrup. Cool completely.
11 - Beat butter until smooth. Gradually add powdered sugar, beating until fluffy. Beat in elderflower cordial. Add milk as needed to achieve spreadable consistency.
12 - Frost cooled cupcakes with elderflower buttercream. Garnish with edible flowers or lemon zest if desired.