Start by heating the olive oil over medium-high heat in a large pan. Once hot, add the minced beef. Stir the meat constantly, breaking up any clumps, until it changes color and all liquid has evaporated. You want to see it lightly browned, which should take about 5 minutes.
Next, add the minced onion and crushed garlic to the pan. Cook, stirring frequently, until the onion turns translucent. This will enhance the aroma and flavor of your filling.
Now, toss in the minced tomato and minced red bell pepper. Stir everything together and cook for a couple of minutes until the vegetables are tender.
Pour in the tomato sauce and mix well. Season with salt and pepper to taste. Cover the pan and let it simmer over low heat for about 10 minutes, or until most of the liquid evaporates. Stir in the minced parsley before removing it from heat.
While the filling cools, preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius). In a medium saucepan, melt butter over medium-low heat.
Once melted, add all-purpose flour all at once. Stir vigorously to combine, making sure there are no clumps. Cook while stirring for about 2 to 3 minutes, until the flour turns a light golden color.
Slowly whisk in the whole milk, continuing to stir vigorously to prevent clumping. After it’s thoroughly mixed, keep stirring on low heat for another 2 to 3 minutes until the sauce thickens slightly, resembling drinkable yogurt. Season with salt and pepper to taste.
Remove the béchamel sauce from heat and let it cool to room temperature. It will thicken further as it cools.
In a lasagna baking pan, pour half of the béchamel sauce, spreading it evenly across the bottom. Fill the uncooked cannelloni with the meat filling using a small spoon. Place the stuffed cannelloni in the baking pan, ensuring they are nicely arranged.
Cover the filled cannelloni with the remaining béchamel sauce, making sure they are entirely bathed. Tightly cover the pan with aluminum foil and bake in the preheated oven for 30 minutes.
After that, uncover the pan, sprinkle shredded mozzarella on top, and return it to the oven. Switch to the broiler setting and cook until the cheese is bubbly and golden brown, which should take a few minutes.
When done, remove from the oven and garnish with more minced parsley. Serve hot and enjoy the comforting flavors of Canelones a la Dominicana with your loved ones!
