Heat cream in a sauce pan just before it reaches a simmer. Remove from heat and add lavender blossoms. Set aside for 10 minutes, strain out the blossoms completely. Transfer back to the sauce pan, cover and refrigerate for an hour. This helps the flavours to develop.
Preheat oven to 325 F. Put the sauce pan back on medium-low heat, add the chopped chocolate, and stir to melt. Continue to stir until the chocolate has dissolved completely. Remove from heat.
Whisk the yolks and sugar in a bowl until thick and creamy. Slowly pour the chocolate-cream mixture into the egg mixture with one hand, while whisking the egg mixture with the other hand, simultaneously. Take care that the eggs don’t get curdled due to the addition of the hot cream mixture. Strain once again.
Line a baking dish (about 9x9) with a clean kitchen towel. Place 4 ramekins without touching each other. Evenly distribute the chocolate mixture among the ramekins. Pour hot water into the baking dish until it reaches halfway up the sides of the ramekins. Carefully slide into oven and bake for 20 minutes. The custard should still be wiggly when pulled out of the oven. Take out of the oven, cool completely, and refrigerate overnight, covering the ramekins with plastic wrap. Serve cold with chocolate shavings or whipped cream.