This is a straight forward variation on Jamie Boudreau's Raspberry flip
3 parts Bourbon
1 part creme de murre
I've always been told when using egg or egg parts to put them in the mixing glass & give it a quick whisk with the bar spoon. So crack an egg into there and beat it to break up the yolk & roughly mix it into the white. Drop in the blackberries (whole) and the ice. Add bourbon & creme de murre. The original calls for peach bitters, I didn't have them so opted to leave the bitters out this time.
Shake HARD strain & serve
You end up with basically a blackberry smoothie, quite dangerously the alcohol bite is hidden away.
Don't be afraid of whole egg, most UK eggs are salmonella free (at least the lion mark ones are). The resulting drink is really worth it. Drink it now before Michelmas when Satan ruins all your blackberries