Remove butter from refrigerator in time and let it soften. Preheat the oven to 180 °C.
Chop the lavender flowers very finely or weigh them with a chopping knife.
In a bowl, mix both types of flour with baking powder, baking soda if desired, the chopped lavender flowers and sugar until well blended.
In another bowl, beat the egg and mix with buttermilk and the softened butter.
Line the muffin tins with melted butter.
Stir the buttermilk mixture quickly into the flour mixture, preferably with a fork, but don’t stir too long so that the mixture stays nice and fluffy afterward.
Immediately fill the muffin cups about 2/3 full and bake in a hot oven for 20-25 minutes until golden brown.