01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with cupcake liners.
02 - In a medium bowl, whisk together the flour, baking powder, and salt until well combined.
03 - In a large bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3 minutes.
04 - Beat in the eggs one at a time, mixing thoroughly after each addition. Stir in the vanilla extract.
05 - In a small measuring cup, combine the elderflower cordial and milk.
06 - Add the flour mixture to the butter mixture in three additions, alternating with the milk mixture. Begin and end with the flour. Mix until just combined, being careful not to overmix.
07 - Divide the batter evenly among the cupcake liners, filling each about two-thirds full.
08 - Bake for 18 to 20 minutes, or until a toothpick inserted in the center comes out clean.
09 - While cupcakes bake, combine the elderflower cordial, water, and sugar in a small saucepan. Heat gently over low heat, stirring constantly until the sugar completely dissolves. Remove from heat and let cool.
10 - Let the cupcakes cool in the pan for 5 minutes, then transfer to a wire rack. Brush the warm cupcakes generously with the elderflower syrup. Allow to cool completely.
11 - Beat the softened butter until smooth and creamy. Gradually add the sifted powdered sugar, beating until fluffy. Mix in the elderflower cordial. Add milk as needed to achieve a smooth, spreadable consistency.
12 - Frost the completely cooled cupcakes with the elderflower buttercream. Decorate with edible flowers or a sprinkle of lemon zest if desired.