In a large stock pot, add the water and bring to a boil. Add the salt. The ratio is 1 tablespoon salt to 1 liter of water.
Place the linguine in the pot and stir until the water returns to a boil. Cook the pasta until tender, but with a bit of resistance (al dente), about 12 minutes.
While the pasta cooks, prepare the sauce. Set a 12-inch saute pan over medium-high heat. Add the butter and olive oil to the pan.
Once the butter has melted, season the chicken with 1 tablespoon of the Essence and add the chicken to the pan.
Sear the chicken in batches until well browned on both sides, about 2 minutes. Remove from the pan and set aside.
Add the onions and cili padi to the pan and saute until the onions are softened and lightly caramelized, about 4 to 5 minutes.
Add the garlic to the pan and saute until fragrant, about 30 seconds.
Add the cream, remaining 1 tablespoon of Essence, ½ teaspoon of salt, and the chicken to the pan and bring to a boil. Cook the sauce until the cream is reduced by half, about 2 minutes.
Add the tomatoes, linguine and the reserved cooking water to the pan and cook, tossing to incorporate for 3 to 5 minutes.
Remove pan from the heat and add the green onions, Parmesan and celery leaves and toss to blend.
Serve immediately.