I brewed something similar before but am confident this will be better. The last batch was brewed without crystal malts and I remember wishing I'd added some to the mash when I was drinking it. A friend and I both agreed "needs crystal". Can't get more crystal than dark crystal!
I also fermented with Harvey's of Sussex yeast last time. This time I'm fermenting with S05 with a high mash temp. Prob around the 74c mark as I also want this to be big and sweet.
The molasses and treacle are for extra richness and depth.
Brought my efficiency down to 75% so that I don't have to push loads of liquor through the mash and boil for hours on end. May even bring this down to 70%. Will see how I feel. It WILL begin at 1.061. I've promised myself that!

Hoping to brew tomorrow...
Oatmeal Stout
Size: 28.0 L @ 20 °C
Efficiency: 75.0%
Attenuation: 78.0%
Original Gravity: 1.061 (1.048 - 1.065)
Terminal Gravity: 1.013 (1.010 - 1.018)
Color: 58.67 (22.0 - 40.0)
Alcohol: 6.25% (4.2% - 5.9%)
Bitterness: 40.2 (25.0 - 40.0)
Ingredients:
5.7 kg (72.3%) Maris Otter Pale Ale Malt - MM - added during mash
900 g (11.4%) Oats Flaked - added during mash
400 g (5.1%) Chocolate Malt - added during mash
230 g (2.9%) Roasted Barley - added during mash
250 g (3.2%) British Dark Crystal - added during mash
200 g (2.5%) Crystal Rye Malt - added during mash
100 g (1.3%) Torrified Wheat - added during mash
100 g (1.3%) Molasses - added during boil, boiled 20 m
50 g Black Treacle - added during boil, boiled 20 m
50 g (100.0%) Northern Brewer (9%) - added during boil, boiled 90 m
Yeast - S05
AMEN