Heat a large sauté pan over medium-low heat. Add the olive oil and heat through then add the butter and allow to melt. Add the breadcrumbs and garlic powder, shaking the pan or stirring constantly until the breadcrumbs are uniformly golden brown, about 4 minutes. Immediately remove from the pan to a bowl or container and store in an airtight container until ready to use.
For the onion soubise:
Heat a large sauté pan over low heat. Add the butter, ½ cup of water, the onions and thyme to the pan. Continue to simmer the onions over low heat, stirring occasionally, until they are tender, about 1½ hours. Season with salt.
For the pasta:
Over medium heat, stir the flour into the onions, cooking until it’s pale brown, about 1 minute. Stir in the beef stock and bring to a simmer. Add the kale and cook until wilted, about 6 minutes.
Place a large pot with salted water over medium heat and bring to a boil. Add the pasta and cook until just al dente, about 8 minutes. Drain the pasta, reserving about 1 cup of the pasta cooking water and return to the pot. Add the onion and stock mixture over the top, stirring in ½ cup of the pasta cooking water.
Heat the oven to broil on high. Spread the pasta in baking dish and top with the gruyere cheese and thyme. Add to the oven and broil until the cheese is melted and bubbly, about 4 to 5 minutes. Remove and top with the buttered breadcrumbs then serve immediately.