My definitions of "inward slanted walls", and "undercut rim" may be different than some others here.
(I am not trying to get others to change their definitions, but these are mine.)
This is an undercut rim:

The undercut rim has an internal surface that is, or is close to
parallel with the top surface where it meets the rim. It can be accomplished with a series of gouges, graduating from 5/8" shaft to a 1/2", and then 3/8 shaft. These gouges will have a double bevel for clearance through the internal curve. The final step is done with a 1/2" scraper (not NR) ground to a curve on the left side and used in an extreme shear mode right up where the inside is near parallel with the top surface, and meets the tip of the rim. It takes a bit of practice, because the final finished surface needs to be as well done as the rest of the bowl.
(Art connoisseurs will notice if it isn't, and they can be very critical of your craftsmanship, if it's not!)
This is an inward slanted wall:

The inward slanted wall is
much easier to do, and has one continuous less intimidating graduating curve from the rim to the center of the bowl bottom. It's done with a 5/8" or 1/2" shaft gouge, and the entire surface can be done all the way from the tip of the rim to the center of the bowl bottom. This also takes some practice, but the main tip I can give, is to learn to rotate the gouge on it's longitudinal axis during the cut. A couple repositionings of the tool rest may be necessary.
(Sometimes extending your gouge off the tool rest is unavoidable, but I like to keep the extension to a minimum.....for better overall control.)
-----odie-----