Preheat the oven to 350°F (175°C). Grease a loaf pan or line it with parchment paper.
In a large bowl, mix the all-purpose flour, whole wheat flour, baking powder, salt, and cinnamon (if using).
Fold the dandelion petals into the dry ingredients.
In another bowl, whisk together the warm milk, honey, melted butter, egg, and vanilla extract. Add lemon zest if using.
Slowly pour the wet ingredients into the dry mixture and stir until combined.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 45-50 minutes, or until golden and a toothpick comes out clean.
Let cool for 10 minutes in the pan, then transfer to a wire rack to cool completely.