Mouth relaxed and half open. Do nothing with your lips at all — no smile, no rounding. Tongue flat in the middle — /u/, as in 'cup'.
Check yourself: This is the LAZIEST sound in English. If your face is doing anything, you are trying too hard.
Watch for: /ɒ/ and /ɑ/. Because it is unmarked, children reach for a stronger vowel.
◆ marks a word that does NOT follow today's pattern — Blumenfeld boxes these on the page. Teach it by heart; do not let the class sound it out and lose faith in the rule.
Say the word, have them repeat it, count the sounds on fingers, THEN write. The count is what stops a child writing the first letter and guessing the rest.