Prep the oven and pan: Heat oven to 350°F (175°C). Line a 12-cup muffin pan with paper liners.
Crush the lavender: Using a mortar and pestle or the back of a spoon, crush the dried lavender until fine.
This releases flavor and avoids chewy bits.
Whisk dry ingredients: In a bowl, whisk flour, baking powder, salt, and crushed lavender.
Cream butter and sugars: In a large bowl, beat butter, granulated sugar, and honey on medium-high until pale and fluffy, about 2–3 minutes.
Add eggs and vanilla: Beat in eggs one at a time, then vanilla (and lemon zest if using), scraping the bowl as needed.
Combine with buttermilk: On low speed, add half the dry mix, then buttermilk, then the remaining dry mix. Mix just until combined. Do not overmix.
Fill and bake: Divide batter evenly among liners (about 2/3 full).
Bake 16–20 minutes, until tops spring back and a toothpick comes out clean.
Cool completely: Let cupcakes cool in the pan 5 minutes, then transfer to a rack to cool fully.
Make the frosting: Beat butter until creamy. Add powdered sugar in two additions with honey, vanilla, and a pinch of salt. Thin with cream or milk to your desired texture.
Taste and adjust honey or salt.
Frost and garnish: Swirl frosting onto cooled cupcakes. Finish with a tiny pinch of lavender or a light honey drizzle.