Pour the peach syrup and vanilla syrup over the ice together so both pool at the bottom.
Tilt the glass and pour the cream soda slowly down the inside wall until the foam climbs near the rim and drops back.
Pour the half-and-half over the back of a spoon so it clouds the surface rather than sinking straight through.
Stir once gently, fan the peach slice against the inside of the glass where it shows, and serve immediately.
Good to Know
Fill small pump bottles with the peach and vanilla syrups ahead of time so guests can pump their own ratio instead of measuring with a spoon mid-party.