Step 1: Place blueberries in 2-quart microwave-safe casserole. Cover and microwave on high for 5 to 7 minutes or until berries are very soft, stirring every 2 minutes. Use potato masher to crush berries. Press through fine mesh sieve, removing seeds and skins. Reserve juice (should have about 1 cup juice).
Step 2: In large saucepan stir together flour, sugar and 2 teaspoons cinnamon. Gradually stir in milk. Cook and stir over medium heat until just boiling. Immediately remove from heat. Gradually whisk in blueberry juice.
Step 3: Immediately pour into six 8- to 10-ounce mugs. If desired, top with whipped cream and additional cinnamon or nutmeg.
Make Ahead Directions: Prepare recipe through Step 1 above. Cover and refrigerate juice for up to 1 week or freeze juice for up to 1 month. Before serving, in small saucepan warm chilled or frozen blueberry juice over medium heat until just hot. Continue with recipe starting with Step 2 above.
