Sunyata

Emptiness by Guy Armstrong for a general approach.

The Fundamental Wisdom of the Middle Way: Nāgārjuna's Mūlamadhyamakakārikā by Jay Garfield

Practicing the View of the Other Emptiness Great Middle Way, "Light Rays of Stainless Vajra Moon

Meditation on Emptiness by J Hopkins

Seeing That Frees: Meditations on Emptiness and Dependent Arising by Rob Burbea

The Emptiness of Emptiness: An Introduction to Early Indian Madhyamika. By C.W. Huntington

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The Theory and Practice of Other Emptiness Taught Thruugh Milarepa's Song
And other writings of Jamgon Kongtrul Yon tan Gyatso
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I found Greg Goodes books and web page very helpful in regard to the Emptiness Teachings...

But start anywhere and don't let go.

https://suttacentral.net/sn35.85/en/bodhi

https://suttacentral.net/mn121/en/sujato

https://suttacentral.net/mn122/en/sujato

https://suttacentral.net/sn43.4/en/sujato

If you prefer to listen/watch than read, try this: https://www.youtube.com/watch?v=AXG8o8gndsI

Do keep in mind that various Buddhist schools, traditions, sects, yanas, teachers, and commentators each have a different approach to explaining what is perhaps the deepest subject in all of reality itself. While I'm certain all of the suggestions here are valid and thoughtful there will likely be glaring contradictions between the view of emptiness which each presents. Such presentations are, perhaps, provisionally correct but they all fall short of the Ultimate Truth which can only be accessed experientially through recognizing your own true nature.

From Access to Insight:

SN 22.95 PTS: S iii 140 CDB i 951

Phena Sutta: Foam

On one occasion the Blessed One was staying among the Ayojjhans on the banks of the Ganges River. There he addressed the monks: "Monks, suppose that a large glob of foam were floating down this Ganges River, and a man with good eyesight were to see it, observe it, & appropriately examine it. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in a glob of foam? In the same way, a monk sees, observes, & appropriately examines any form that is past, future, or present; internal or external; blatant or subtle; common or sublime; far or near. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in form?

"Now suppose that in the autumn — when it's raining in fat, heavy drops — a water bubble were to appear & disappear on the water, and a man with good eyesight were to see it, observe it, & appropriately examine it. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in a water bubble? In the same way, a monk sees, observes, & appropriately examines any feeling that is past, future, or present; internal or external; blatant or subtle; common or sublime; far or near. To him — seeing it, observing it, & appropriately examining it — it would appear empty, void, without substance: for what substance would there be in feeling?

And so it continues for the other skanda.

Perhaps recite the heart sutra a good number of times while having some faith and receptivity for the meaning of it permeating your mindstream in the best of ways. FWIW.