- Draw a box with 4 sides.
- Use the Anchor Point Tool (shift + c) to select the top line and drag it. The adjacent points will split their anchors.
You can use the Anchor Point Tool to convert points between corner mode, mirrored anchor mode, and split anchor mode. Not sure if those are the official terms.
And make sure to tell us how long it took you. In SVG Path Builder the toast shape above took me 10 seconds, and it never gave me grief by trying to curve the sides, while still giving me the guides for each of the relevant corner nodes. Drawing that in Inkscape is just as easy. Same for CorelDraw.
If you can manipulate the guides of your corner nodes and have them affect only the top side, then you've succeeded in making those two top corner nodes cusp. I have never seen anyone online showing cusp nodes in Illustrator.
Again, the anchor point tool is necessary here. First you drag the top line up to add split anchors (or cusp nodes, haven't ever used that term) to the two adjacent points. Then you can use either the anchor point tool or the direct selection tool to adjust the two new anchors.
The anchor point tool is essential to using Illustrator. You can read more about it under "Convert an anchor point precisely using the Convert Anchor Point tool" here: https://helpx.adobe.com/illustrator/using/editing-paths.html
One feature Adobe Illustrator is sorely lacking (afaik) is grid snapping for anchors. They will snap to objects, lines, and points, but grid snapping would be really helpful.