Gluten Free Lamb Shanks Braised in Red Wine

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  4 bone-in lamb shanks (about 1 lb / 450g each)
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  1 ½ tsp kosher salt
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  1 tsp black pepper, freshly ground
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  3 tbsp olive oil, divided
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  2 medium carrots, peeled and cut into 1-inch pieces
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  2 stalks celery, cut into 1-inch pieces
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  1 medium yellow onion, roughly chopped
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  4 cloves garlic, smashed
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  2 tbsp tomato paste
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  2 cups dry red wine (such as cabernet sauvignon or côtes du rhône)
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  2 cups beef broth
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  1 can (14 oz) diced tomatoes
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  3 sprigs fresh rosemary
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  4 sprigs fresh thyme
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  2 bay leaves

For the slurry

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  2 tbsp cornstarch
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  3 tbsp cold water

For serving

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  2 tbsp fresh flat-leaf parsley, roughly chopped (optional)