Measure and add all coulis ingredients(: mixed berries, sugar and water) to medium sauce pan over medium-low heat with lid on for 3-5 minutes. Remove lid, occasionally stir and let berries begin to break down until water begins to evaporate and mixture starts to reduce.
Pour cooked berry mix into a blender or food processor and purée for about a minute.
Pour purée through a sieve using a rubber spatula pass the purée through. Disgard leftover seeds and set aside purée.
Measure and mix egg yolk, (separate and set egg white aside for later!*) sugar, cornstarch and vanilla extract until well blended and set aside.
Heat milk in a medium size sauce pan over medium low heat until it begins to simmer
SLOWLY begin to whisk small amounts of heated milk in with the egg yolk mixture to temper it. If you add it all at once you will scramble the yolk, adding it slowly prevents this. Pour the combined mixture back into the sauce pan and quickly whisk over medium heat until it becomes thick and creamy (this happens fast). Once it thickens remove from heat. Pour pastry cream into a bowl and lay plastic wrap over the pastry cream to keep it from oxidizing and developing a skin.
Measure out needed amounts of pastry cream and mixed berry coulis for soufflé batter. Mix until well combined and refrigerate until completely cool (about 20 minutes). (Refrigerate the remaining pastry cream and set aside the rest of the coulis to pour on top of soufflés!)
Preheat oven to 360°
Brush a thin layer of room temperature butter in upward vertical strokes and all over sides and bottoms of the ramekins. Make sure to brush in upward vertical strokes because it helps ensure a good rise of the souffle. Chill the buttered ramekins for 1 minute to let the first layer of butter set.
While the butter is setting prepare chocolate coating of the soufflé by blending them in the food processor for about 45 seconds.
Repeat and butter ramekins with the same vertical strokes. Add shaved chocolate to the ramekins and gently roll the ramekins to evenly coat the entire inside surface with chocolate. Pour excess chocolate shavings into remaining ramekins until they are all nicely coated. Refrigerate ramekins to let butter and chocolate shavings set.
Pour measured egg whites into a stand mixer with whisk attachment and begin blending egg whites on a medium speed. Once egg whites begin to look foamy squeeze in lemon juice (do not stop mixer to add lemon, let it continue to whisk). When the volume has doubled slowly and gradually begin to add sugar. Lightly add the sugar so evenly disperses throughout the meringue instead of sinking to the bottom of the bowl. Increase speed to high until meringue forms stiff peaks and looks a little glossy and bright white (picture for reference in post).
Using a rubber spatula gradually fold in ⅓ of the mixed berry coulis/pastry cream mixture until it is well incorporated. Do this in a careful folding motion so you do not deflate the meringue! The meringue will lose a bit of height, but that is normal!
Scoop a heaping portion of the berry soufflé into your chilled ramekins and gently tap the ramekin to even out the batter and level/scrap off the excess batter. Clean the rim and outside of the ramekin. Lastly, using your finger create a small edge along the rim of the soufflé (this ensures a more even/straight rise).
Place ramekins on a baking sheet and place them on the center rack of the oven with room to grow. If you're using a 6oz ramekin they take about 10-12 minutes, bake until the top is a golden brown. If you are using a 10oz ramekin it takes closer to 15 minutes.
While soufflés are baking prepare plates, a sieve with powdered sugar and the berry coulis sauce toppings.
Remove from oven and place ramekin on serving plate. Pour berry coulis on top and dust with powdered sugar! Serve immediately, and ENJOY!