I used to make my own marmite - you can choose the thickness/texture you prefer by adjusting the ingredients.
It's simply flaked yeast (not brewers or bakers yeast - you need the flaked, edible variety) and mix it with soy sauce.
Now, soy sauce comes in several varieties - light, dark, mushroom are most common, so experiment a little, see which flavour you like best. I personally prefer the taste of mushroom soy with my yeast, though again, the flavour can vary with different brands.
However, the flaked yeast supply in NZ has dried up!!!!
It's made in Aus and they're not sending it over. In fact, I haven't been able to get any since about August last year. I was told it would be back in supply by christmas but they didn't specify which year. In the meantime I'm having to use a powdered variety but it's rather bitter and not nearly as nice.
And yes, always spread the marmite on your toast before the butter!
Robyn