So as per the following wiki article;
Sickening Blast"Note that unlike other variations of warlock, this spell can't be paired with eldritch blast shapes."
Which implies that Blast Shapes and Essences can otherwise be combined as per PnP allowances. However, having only just unlocked both Chain and Beshadowed Blast, there's no sign that you can combine any Shapes and Essences at all; other Warlock players have said they weren't even aware that this was how it was meant to function.
As shown here, the spell list shows both a Blast Shape and Blast Essence, but no option to combine them.
Assuming we're using the 3.x implementation onwards, Warlock Eldritch Blast should be able to benefit from both a Shape and an Essence, one of each, both able to be combined. Examples being Eldritch Chain + Vitriolic Blast, Eldritch Cone + Beshadowed Blast, etc.