For béchamel: Melt butter in a large saucepan over medium heat. Once melted, stir in flour until smooth. Continue stirring as flour cooks to a light, golden, sandy color, about 7 minutes.
Increase heat to medium-high and slowly whisk in milk until thickened by the roux. Bring to a gentle simmer, then reduce heat to medium-low and continue simmering until flour has softened and no longer tastes gritty, 10 to 20 minutes. Season with salt and nutmeg. Makes 2 cups.
Chef's tip: With leftover béchamel, consider making a cheese sauce by reheating and stirring in grated cheddar cheese during the last 2 minutes of cooking, along with a pinch of cayenne pepper.
For dip: Heat oil in a sauté pan. Sauté spinach and shallots until spinach is slightly wilted. Add salt to season. Add sun-dried tomatoes, cheddar cheese and béchamel and heat until cheese is melted. Place in a small gratin dish and top with grated parmesan. Place under the broiler until golden brown, 5 to 10 minutes. Serve with grilled toast, pita chips or crackers.
Note: Another variety spinach variety may be substituted; however, Bloomsdale tends to be sweeter and holds up better when sautéed.