Heat a large frying pan over medium-low heat. Add the olive oil and butter. Add the onions. Cook over medium-low, stirring occasionally until they are caramelized. To get them really nice and truly caramelized it takes about an hour. Low and slow is the way to go with onions. This is mostly hands-off time, just make sure to stir them every 10 minutes.
You can caramelize the onions the day before making the tarts. Just pop them in the refrigerator.
Meanwhile, preheat the oven to 350. Put the mozzarella and cream cheese in a microwave-safe bowl. Microwave one minute. Stir. Microwave 30 seconds. Stir. At this point all the cheese should be melted. Microwave 30 more seconds until uniform and gloopy (it should look like cheese fondue at this point). Add the rest of the dough ingredients and the cheese to a food processor. Mix using the dough blade until a uniform color. If you do not have a food processor you can mix in a medium bowl with a wooden spoon but you may need to dump it onto wax paper and knead it by hand to thoroughly incorporate the ingredients.
Grease a 24 hole mini muffin tin. Divide the dough between the holes of the tin. Using wet fingers press it down into the bottom and up the sides of each hole. If your fingers aren't wet it will stick to your fingers. I keep a small bowl of water next to me while I work. I dip my hands, press two out, dip again, and repeat.
Once the onions are a golden brown turn off the heat and stir in the Finlandia Black Garlic Creamy Gourmet Cheese.
Bake the tart shells for 6 minutes. Remove from the oven and divide the onion mixture between them. Top each with ⅙ of a slice of Havarti. Bake for 25 minutes until the cheese is bubbly and the crust is golden.
*** If you cannot find this soft cheese you can sub in 6 oz cream cheese softened and mixed with 1 oz heavy cream and 1 tsp garlic powder