1 Tbsp. olive oil
Melt the butter in a pan and then add the flour, whisk for 1 minute. Gradually whisk in the milk. Be patient with this step because you don't want your sauce to have lumps in it. Bring the sauce to a boil so it thickens slightly. Add nutmeg and cool just enough so you can blend it. Put half the sauce in a blender and add the basil. Blend until smooth. Then add it back to the rest of the sauce. Season to taste.
Lightly butter a 13 by 9 by 2 inch pan. Spread some sauce on the bottom of the dish then add 3 lasagna noodles. Spread the squash over the noodles and then sprinkle with mozarella cheese. Pour more of the sauce over the noodles. Repeat layering 3 more times.