In a wide skillet, add the butter and olive oil and heat over medium heat until the butter begins to melt. Add all the onions along with 1/2 tsp of kosher salt. Cook for 3 to 4 minutes over medium heat until the onions begin to soften. Then turn down the heat to medium low.
Cook the onions over medium low heat until they are very tender and a deep brown colour. Keep an eye on the onions, stirring regularly, to ensure they caramelize evenly and do not stick to the pan. Add a bit more olive oil if the onions begin to stick. Transfer to a separate bowl and let cool before assembling.
Preheat the oven to broil on high. Thinly slice the baguette on a bias and arrange on a baking sheet. Broil the crostini for 3 to 5 minutes until golden brown. Flip the slices and broil the other side until golden brown. Keep an eye on them as they can burn easily. Set aside.
In a food processor combine the goat cheese, cream cheese, and 1/2 tsp kosher salt. Blend the cheese, stopping to scrape down the sides once or twice until completely smooth and creamy. Set aside.
Preheat the oven to 400°F. Lightly spray a gratin dish with non-stick spray. Drop small dollops of the whipped goat cheese into the dish, using about 1/3 of the cheese. Drop spoonfuls of the onions around the cheese. Lightly drizzle with honey and sprinkle with some of the chopped thyme. Repeat the layers two more times.
Bake the goat cheese for 20 to 25 minutes until the cheese is bubbling around the edges and beginning to brown on top. Serve the baked goat cheese with the toasted crostini and enjoy!