Preheat oven to 350. Line a sheet pan with parchment paper. Set aside.
In a large dutch oven, heat butter and olive oil over medium heat. Once the butter has melted, add the flour. Cook, stirring often, for 2 minutes. Add in the onion, celery and carrot. Cook, stirring often, until onions begin to soften, about 5 minutes. Add in the potatoes and stir to combine. Pour in the milk and heavy cream. Stir to combine to ensure there are no lumps and then add the stock. Turn the heat to high and bring to a bubble. Once bubbly, stir in the shredded chicken. Turn the heat to low and let cook, over a low heat, stirring every now and then, for 15 minutes. In the meantime, make the garlic-Parmesan oyster crackers.
Place the oyster crackers in to a small mixing bowl. Set aside.
Melt butter in a large saute pan over medium low heat. Once melted, add the garlic and parsley. Let cook for a minute or just fragrant being careful not to brown the garlic. Pour the warm garlic butter over the oyster crackers. Stir to coat them in butter mixture. Once coated, add in the parmesan cheese, salt and black pepper. Toss to coat and spread them on to the parchment lined sheet pan. Bake in the oven for 5-7 minutes. Remove from oven and let cool.
After 15 minutes, the chowder should thicken up a bit it. Add in the frozen corn and peas and cook for a 5 minutes more.
Ladle the chowder into bowls and top with hot sauce, a handful of garlic-parmesan oyster crackers and some coarsely chopped celery leaves.
Grant Melton is an Emmy Award-Winning Producer of the Rachael Ray Show, food writer and recipe developer. He's a contributor to Food52, Food Network Kitchen and Rachael Ray Every Day Magazine. He loves cookies, cocktails and kindness.