BASE MALT: obviously, I should be using MO, but I don't have it to hand, so I'm adding ~2% vienna and ~2% munich to the pilsner base to increase complexity. I also have torrified wheat and oats that I need to use up. I'll put equal amounts in.
SPECIALITY MALT: My situation is that I need to use up a bunch of mixed malts. I am planning to split the base wort in two and, having separately steeped and boiled two different speciality malt bills, add these to two different fermenters. To maximise the difference between the two resultant beers, one will be on the light side the other on the dark...
I developed a very simple formula using the average colour of the speciality malts. It is based around a BYO article on English bitter, that containing three principles:
1) Speciality malts can have a colour of 40-150L.
2) These should not exceed 10% of the grist.
3) The higher the colour, the lower the percentage of grist: "A bitter with 10% 150 °L crystal malt may not be cloying, but it can be too intense a flavor for this style."
For a starting point, I decided that a 150L malt cannot exceed 7.5% of grist. Then just took a linear scale based on that.
Speciality Malt grist 1:
0.15kg Crisp Crystal 100
0.65kg Dingemans Aromatic