Cutting underlining: wrong or right way?

I sinned, readers. I cut my underlining and fashion fabric together!

Was it wrong? Well, when I took an underlining class with Sarah Veblen, I learned that underlining and fashion fabric must be cut separately.

You may ask, why? The answer is the grain. You may have aligned your lengthwise edges properly so the pattern can easily be laid out. However, your crosswise grain may be off, and you won't even notice it...

But listen to this story:

...  I mentioned earlier that I was (am still) working on a fitted strapless guipure dress during the couture class in Baltimore. Once the inner foundation was fitted and constructed I had to cut the underlining for the guipure. The lace was grey and I wanted to use peach charmeuse to underline it. I wanted some shine to peak through the lace to make contrast between the background and the lace more evident, but charmeuse was too light for this relatively heavy lace. Crepe back satin, which is heavier than charmeuse, was not available in the color and was three times more expensive...

Here is the sneak peek of my dress at a more advanced stage - I was applying guipure lace to the charmeuse/muslin foundation and sculpting it over a tailor's ham for shaping.

By the way, some of you may have recognized the lace - I was considering it for another project but never dared to cut into it. Couture school last week was a perfect opportunity!

The solution was to back charmeuse with some heavier fabric, and so I decided to use plain muslin, or calico, for this purpose. Now, I was working on a time crunch. Finishing the dress was not my goal, but I wanted to learn as many techniques as possible. So, cutting two underlinings separately would take ages! I would have had to mark grain on both pieces, so when they were joined they would align perfectly. Imagine how much time would it take!

So, I decided to cut them together. I had a large rectangular table at my disposal, and so I grained the muslin layer first, aligning the lengthwise AND crosswise edges along the table edges. Then, I made sure that the charmeuse crosswise edge was indeed cut on crosswise grain. Next, I laid charmeuse over the muslin and carefully aligned all the pieces making sure both layers were smoothed out and grained.

Finally, I pinned the prepared muslin pieces to the two layers and cut them. Yay!

In my opinion, this was way more accurate than cutting both layers separately, because charmeuse is relatively tricky and moving it around without support is a recipe for  disaster.

With muslin under the charmeuse I could easily cut it and move the pieces to my sewing table and thread-trace them!

If you decide to make it the same way, make sure to grain both the lengthwise AND the crosswise grain of both layers and align them accordingly! 

By the way, I used the same technique for my Clover pants (the image above)!

And, yes, I am sure someone else has done it this way before I reinvented the wheel. I am still happy I found a shortcut. (ooups, another S* word - you are not supposed to have shortcuts in couture.)

How do you cut your underlining, readers?