malachi wrote:For what it's worth...

I've tuned my approach over time. The old approach (as detailed all over the place) was a good starting point. But some things turned out to be either inefficient or poor at dealing with edge cases.

I try to start with some constants that are as likely as possible to be accurate for the majority of coffees. In this case, I start with an LM ridged double basket and a target volume of between 1.75 and 2.0 oz with a moderate flow rate (somewhere around 25 seconds for that volume though I evaluate by flow not time).

I'll also try and understand the "signature taste" of the coffee.
The "signature taste" requires some knowledge of the roaster's style and the desired flavour profile of the coffee. Is the person roasting this coffee a fan of low acidity espresso? Are they a "chocolate bomb" aficionado? If you know what they like out of their espresso you can do minor adjustments to your dose. In many cases (these days) you can use the interwebs to research and find out what the roaster looks for. Otherwise, go by the retail location of the roaster and taste the shots.
This allows me to understand what I'm "shooting for" in the cup.

Once I have this information, I'll start making some guesses on the variables.

My initial goal is to make a quick guess on dose volume.
I do this based upon the coffee (the bean/blend composition.)
If the coffee seems likely to have low pH (has robusta or aged coffees or a lot of naturals) I'll start with a down dose. If it seems likely to have a moderate pH (pulped naturals, a mix of naturals and washed coffees) I'll go with a moderate dose. If the coffee is high pH (mostly high-grown washed arabica) I'll up-dose.
This baseline is then slightly impacted by degree of roast (for a darker roast I'll drop the roast a percentage, for a lighter roast I'll up it).

Once I have a starting point for dose, I'll try to come up with a starting point for brew temp.
I'll evaluate the coffee for two characteristics. First - roast degree and second - bean composition.
With the former, I tend to make some quick rough decisions. If the roast is light, I tend to start with a baseline temp of 202F. If medium, I will stick with 200F. If dark, I'll drop it down to 197F.
Now... I'll also adjust this based on the bean composition. If, for example, I'm working with high-grown washed arabica I'm going to reduce the brew temp. If I'm working with aged or monsooned coffees I will up the brew temp (both from the baseline above).
So a light roasted coffee with monsooned beans will move up to 203F as a starting point.

Once I've got temp and dose I dial in the grind and then I'll start experimenting.
I always start by re-evaluating temp. So I'll pull a shot and evaluate it for brew temp. Is it alkaloid? Is it thin? Is it sour? Astringent? Based on the taste, I will alter the temp by small degrees to find the sweet spot. I'm not looking for a great shot here -- I'm just looking for the right brew temp. The idea is to get the balance of sweet, sour and bitter. If any of these dominate too much, I need to change brew temp.

Once I've found what I feel is the brew temp sweet spot, I'll start working on dose.
The way I tend to do this is focus on two things. First - clarity of flavour and second - roundness and balance.
If the cup is "muddied" I'll reduce the dose. If the cup isn't fully developed and sweet and rich I'll up the dose. Mouthfeel is one of the critical attributes I'm looking at here - as is sweetness and definition.

This is usually enough. It usually gets me to the point where I have a shot that I feel matches well with the signature profile and optimizes the coffee.
Now... that doesn't mean I like the shot. There are coffees that I just don't like. It means that I feel like I have a cup profile that fits the coffee.

But there are exceptions. There are edge cases where all the above doesn't get me to where I want to be with the coffee.
It's usually only at this point that I start looking at changes to extraction volume and basket size.

For example, I've found that some lighter roasted delicate coffees tend to end up poorly developed no matter what I do - especially when they are pulped naturals. But if I then swap to a triple basket and deliberately down-dose (19 grams) I "open up" the coffee and it becomes more defined and clear. Or with monsooned coffee I find that the only way I can get the desired sweetness without getting a "wet cardboard" aftertaste is by going with a triple basket, normal dose and then pulling a ristretto shot. Sometimes I find that some high-grown washed coffees are best pulled very short and slow. The same is true of some Indonesians.
You get the idea.