Formation of a bubble which is not a sphere
Surface tension will relax most or all bubbles into a
spherical shape around internal pressure.  So, one solution is to create a situation where surface tension is nonuniform:a bubble adhering to the wall of a glass. Because the glass is not part of the liquid's surface, that
face of the bubble needn't be spherical.

Another is to modulate the pressure the film contains.  Two bubbles in collision is the
easiest way: if the bubbles are the same internal pressure, they
will form a flat wall where they meet.  If they do NOT have the same
internal pressure, the wall curvature is concave toward the
center of the smaller bubble.