Bring a pot of 4 quarts water to boil. Add 2 tbsp salt and ½ tsp baking soda before tossing in the potatoes. After 12 minutes, transfer potatoes to a bowl and let cool for ~10 min, making sure to drain off excess moisture. Sprinkle with a few pinches of salt and pepper.
Meanwhile, add the 2 cloves regular garlic, 1 bulb black garlic, and minced rosemary to ~5tbsp olive oil in a small pan. Cook on the stove on medium until the regular garlic becomes slightly golden, about 1-2 min. Now, pass this through a strainer to separate the solid ingredients from the oil (but reserve both).
Preheat oven to 425 degrees.
At this point, roughly toss the potatoes with the infused oil (by tossing them roughly, a mushy crust ends up on the surface). Cook in oven for 20 minutes. Then flip them and slightly smash down each of them with a fork. Cook for another 20 minutes or until golden brown on all sides.
Meanwhile, combine all ingredients for the Black Garlic Sauce in a food processor or cup with immersion blender. Blend until a smooth creamy consistency.
When the potatoes are done, lightly toss with the reserved minced garlic/rosemary mixture from before. Drizzle over the black garlic mixture and serve.
Notes
Of note, the black garlic sauce make more than you need for this recipe. It keeps really well in the fridge so we just stored the extra and used it for other recipes