PREPARATION: Preheat oven to 350F. Place rack in top third of oven. Grease a 9” quiche dish or pie plate with butter and sprinkle evenly with the breadcrumbs. Set aside.
SAUTÉ THE VEGETABLES: Add the remaining 2 tablespoons butter to a medium skillet and melt over medium-high heat. Tip in the leeks and fennel; sprinkle with a pinch each salt, pepper, and crushed red pepper. Cook, stirring regularly, for 10 minutes or until vegetables are tender. Add the garlic and cook another minute. Spoon the vegetables evenly into the prepared quiche dish and let cool a few minutes.
LAYER IN THE SALMON AND CHEESES: Scatter the salmon over the leek mixture, dot with the cream cheese, and sprinkle with the Cheddar.
WHISK TOGETHER LIQUID INGREDIENTS AND POUR OVER THE CHEESES: In a large mixing cup or medium bowl, whisk together the eggs, milk, cream, ½ teaspoon kosher salt, 1/2 teaspoon fresh ground pepper, and 4 drops (or more) Tabasco sauce. Slowly pour the mixture evenly on top of the cheeses.
BAKE for about 35 minutes or until barely set (a little jiggly at center) and the crust is golden. Don't over bake. Remove from oven to rack and sprinkle with Parmigiano-Reggiano. Rest 10 minutes before cutting and serving warm. Also lovely at room temperature or cold.
Store cooled leftovers for a day or two well-wrapped in the fridge, keeping in mind your fish was already perhaps a day old when you began.