Recently I saw a post where someone wanted to create a background with a
border on the top and left side and have the inner corner be a nice smooth
curve instead of a 90 degree corner. Somebody posted a link to a web page
with a tutorial on a really easy way to accomplish this, and I would really
like to find it again. The steps of the tutorial involved drawing two
rectangles (one on the left and one on top), joining them so they are one
path, drawing another rectangle with rounded corners so that one of the
rounded corners is over the sharp corner, and then using the Combine Paths
tool somehow. I've tried to figure it out, but I can't.

Can somebody point me to that tutorial (or one similar to it)?

Thanks.

Steve