For the savory rosemary tart crust, mix together the flour, rosemary, salt, and garlic powder in a large bowl. Grate the frozen butter over the bowl, pausing to mix in the butter shards every 30 seconds so they don’t just form a large butter clump on the top of the bowl. Add the cold milk and then the water, 1 tablespoon at a time, stirring the dough with a wooden spoon and then working it slightly with your hands to incorporate all the flour. If it doesn’t come together, add another tablespoon of cold water and mix, repeat if necessary until a solid dough forms. Wrap with plastic wrap and refrigerate for 30 minutes before rolling it out until it is about 1/4 inch thick, making a circular shape that is at least 11 inches in diameter.
Transfer the rolled up dough onto a well-greased and lightly floured 9-inch tart pan. Press the dough into the pan, trimming off the excess, and prick it all over with a fork. Cover it and place it in the freezer for 30 minutes. Preheat the oven to 350º F. Grease a sheet of tin foil and gently press it into the crust, forming the sheet of tin foil to the shape of the crust. Place it in the oven and pre-bake the crust for about 15 to 20 minutes, or until it is still very pale but begins to look more crust-like than dough-like. Remove and allow to cool for 5 minutes before removing and discarding the foil.
For the caramelized fennel and goat’s cheese filling, cut the fronds off of the fennel bulbs and cut the bottom 1/4-inch off the bulb. Slice the bulb vertically into about 5 slices. Mince the fronds for the minced fennel fronds listed in the ingredients, set aside. Melt the butter in a large frying pan over medium heat. Add the sliced fennel bulbs and sauté until transparent on both sides and softened, about 15 to 20 minutes.
Preheat the oven to 375º F. In a medium saucepan, heat the milk over medium low heat until hot but not boiling, stirring every couple minutes to keep the milk from scalding. Add the crumbled goat’s cheese and continue stirring until it is completely melted and smooth. Remove the pan from the heat and ladle a scoop of the milk mixture into the bowl of whisked eggs, whisking constantly. Repeat until half of the milk mixture is in the egg bowl. Empty the custard mixture into the pan and place it back over the heat, stirring every minute for 3 to 5 minutes until it thickens. Remove from heat and stir in the salt, pepper, garlic powder, and fresh fennel fronds.
Pour the goat’s cheese mixture into the tart pan so that it is half full, then arrange the fennel bulbs in the pan. Add a bit more goat cheese filling if necessary, taking care to pour around and not over the bulbs. Place the pan in the oven and bake for 45 to 50 minutes, taking the tart out at the 30 minute mark to lightly brush the top of it with an egg wash and then placing it back in. When the filling and fennel bulbs are deeply golden and the filling is set, it is ready. Remove and allow it to cool for 10 minutes before serving.
