Lets start with the sauce so it has some time to cook. In a medium saucepan over medium low heat, add the butter and allow it to melt. Add in the garlic and cook until lightly browned. Be aware that garlic cooks very quickly and trust me, you do not want to taste burnt garlic so keep an eye on it. Add in the flour whisk until well combined, it will bind together. That right there is called a roux and is a the versatile base to many sauces! Next, whisk in the tomato paste until well combined and cook for a minute or so. Continue whisking and slowly add in the milk. All of the ingredients will combine as the milk warms. Add the basil, salt and pepper. Be sure to whisk every few minutes to help work everything together. The sauce will thicken as it simmers. Once it comes to a simmer let it simmer for about 15 minutes or until thick enough to coat the back of a spoon.
While the sauce is cooking you can start the rest. Cook the pasta until al dente and drain. On a baking sheet lined with parchment arrange the noodles in a single layer so they do not stick together.
Now lets get to that fantastic filling! While the pasta is cooking heat a couple of tablespoons in a sauté pan. Add sliced garlic and sauté until fragrant. Add the spinach and cook until wilted. Set aside in a large bowl. Allow the spinach to cool slightly. To the bowl, add in all but a couple handfuls of the mozzarella, ricotta, grated cheese, egg, and salt and pepper to taste. Mix until well combined.
Assembly time!!! First go ahead and preheat the oven to 375 degrees. Ok, take a lasagna noodle and spread a thin layer of the filling on and roll 'em on up.
Grab a baking pan and add in a couple ladles full of the sauce, enough to just coat the bottom. Place those beautiful bundles into the baking pan. Repeat with all the noodles. Pour enough sauce to go about 3/4 of the way up the lasagna rolls. Top with the mozzarella you set aside earlier.
*Note: you may have a few extra noodles and a little extra sauce- thats what I snack on while making this*
Bake for about 20 minutes until hot, bubbly and a little browned on top.