1. In a small saucepan over low heat, bring the milk to a simmer. Remove from heat and add the lavender. Set aside to steep for 60 minutes. Strain the milk through a fine-mesh sieve set over a bowl, then discard the lavender. Add more milk if needed to measure out 1/2 cup (120ml).
2. Preheat the oven to 350°F. Grease a 9-by-5-inch loaf pan with butter, line the bottom and sides of the pan with parchment paper, and grease the paper.
3. In a large bowl, sift together the flour, baking powder and salt.
4. In another large bowl, combine the sugar and lemon zest. Massage together with your fingertips to release the oils. Whisk the eggs, oil, milk, creme fraiche/sour cream and lemon juice, until combined.
5. Gradually add the wet ingredients to the dry ingredients and whisk until there are no lumps and the batter is smooth. Toss the raspberries with a tablespoon of flour, gently fold in the berries.
6. Pour the batter into the prepared pan and smooth the top. Bake for 60-70 minutes, or until a cake skewer inserted in the middle comes out clean. 
7. Allow the loaf to cool in its pan for 10 minutes before transferring to a cooling rack to cool completely.

To make the glaze

1. Sift the powdered sugar into a bowl. Make a well and add the butter.
2. Mix in the lemon juice, black raspberry and culinary lavender. Mix until desired consistency.
3. Pour over the loaf and allow to set.