Preheat the oven to 170°C. Line a large baking tray with baking paper.
Beat the butter and sugar together in a large bowl until light and fluffy, then beat in half the lavender flowers.
Mix in the flour and the ground almonds until well combined. Stir in the chopped toasted almonds and 100g chocolate. The mixture should be a soft dough. If it is sticky, gradually blend in more flour until the right consistency is reached.
With floured hands, shape portions of the mixture into crescents about 8cm long and 2cm thick in the middle and arrange on the prepared baking tray.
Bake in the preheated oven for 15–20 minutes, until lightly golden.
Leave to cool on the baking tray for 10 minutes, then transfer the biscuits to a wire rack to cool completely.
Melt the remaining chocolate in a heatproof bowl, set over a pan of gently simmering water, making sure the bottom of the bowl is not in contact with the water.
Using a fork, drizzle melted chocolate over the top of each biscuit. Sprinkle over the remaining lavender flowers and leave until the chocolate is set.
Store in a cool place in an airtight container.