Creating a rounded shape with a flat base

I’m a beginner. A couple of times, I’ve wanted to create a shape that is a specific flat shape on the base, and is otherwise rounded. For example, if the base were round, it would be a hemisphere. But I do not know how to go about making a shape like that if the base is more complex. Kids’ sand molds are often in this type of shape, for example in this image of a turtle:

Kids’ toys also often have things like stars and moons in this type of shape.

Is there a good way to make this type of shape in general, or would it depend a lot on the shape of the base? I thought at one point that I could cut something completely round in half, but I also do not really know how to make the round thing either.

Well you can start with a rounded shape, and just cut it in half on the horizontal axis, and remove one part to make it flat :wink:

I think what you might be talking about is Auto Smooth.

This is a hemisphere set to smooth with Auto Smooth on

using bezier curves you can draw the shape and then you can either grid fill or fill the shape selecting vertices and using the F to fill the space… Grid fill should be better as you can decide the cuts… Also you should draw only half of the model, the use mirror to generate the other half…
If you want to have different forms on each side then after the mirror you can move the vertices