Preheat oven to 350˚F. Grease a standard 8x4 loaf pan well with butter or oil.
Pick the flowers off of the stems of the elderflower heads. NOTE: The stems of the elderberry plant contain toxins so remove as much of the green stems as possible.
Add the milk and flowers to a saucepan and bring milk to scalding temperature (just before it boils). Remove from heat, cover the pan, and let the flowers steep in milk for 5 minutes.
Meanwhile, whisk together flour, sugar, baking powder, baking soda, and salt in a mixing bowl.
Strain the infused milk through a fine mesh strainer. Measure out 120g or 1/2 cup of the elderflower milk for the cake batter. If you have less than needed, just add more milk.
Whisk together the elderflower infused milk, honey, oil, lemon juice, lemon zest and vanilla extract in a separate mixing bowl.
Add wet mixture to dry mixture and stir together with a rubber spatula until just combined.
Pour the cake batter into the prepared loaf pan. Bake for about 35-40 minutes until cake is golden brown and comes away from the sides and a toothpick inserted in the center comes out clean.
Allow cake to cool in pan for 10 minutes then run a butter knife along the sides to loosen the cake from the pan. Invert cake onto a cooling rack and tap bottom of loaf pan to release the cake if necessary. Remove the loaf pan then invert cake again so it is right side up.