Preheat the oven to 425 degrees F (220 degrees C).
First, prepare the Asparagus (1 bunch). Snap the tough ends off the asparagus and discard. Bring a medium pot of water, big enough to hold all of the asparagus, to a boil. Have the ice-bath next to the stove.
Add the asparagus to the boiling water and cook until al dente and bright green, about 2-3 minutes. Immediately transfer to the ice-water to shock. Remove and set aside until needed.
Lay the Puff Pastry (2 sheet) on a baking sheet that's been covered with parchment paper. Fold over the edges of the dough to make a 1/2-inch crease and seal with the spikes of a fork. Using the fork, poke holes 6-7 times on the bottom of the puff pastry.
Bake for 10-12 minutes, until the dough starts to brown and becomes flaky. If it puffs up too much, use the back of a wooden spoon to carefully deflate. Set aside until needed.
While that is baking, heat Olive Oil (1 tablespoon) in a small saute pan over medium heat. Add the Shallot (1), Garlic (2 clove), and Crushed Red Pepper Flakes (to taste) and saute until fragrant and the onion is soft, about 2 minutes. Set the onion mix aside and clean the pan.
Return the pan to the stove, keeping the heat to medium. Melt the Butter (2 1/2 tablespoon). Add the All-Purpose Flour (4 tablespoon) and mix with a wooden spoon until incorporated. This is your roux. Cook 2 minutes, until you no longer smell flour and only smell butter.
Slowly whisk in the Milk (2 cup). Keep whisking to avoid any lumps. Bring the heat to medium-high and stir until milk thickens. When ready, the bechamel will coat the back of a spoon without running. This will take 4-5 minutes.
Strain the bechamel and discard the lumps left behind. Stir in Pecorino Romano Cheese (3/4 cup) and the onion and garlic mix and stir until cheese is melted.
Add sprinkles at a time of Ground Black Pepper (to taste) and keep tasting and adjusting as needed. Add, taste, and adjust Garlic Salt (to taste) as needed.
Evenly spread a ladle full of cheese sauce into the tart as if it were a pizza. Arrange asparagus slices onto the tart, then sprinkle with the remaining Olive Oil (1 tablespoon) and Pecorino Romano Cheese (1/4 cup).
Bake for 12 minutes until asparagus is roasted, cheese is melted, and the pastry is golden brown.