Make the sauce firstIn a medium pot, add 2 cups milk. Heat over medium-high heat until very hot (doesn't have to be quite boiling). Watch carefully so you don't scald the milk.
Meanwhile, combine the other ½ cup milk, flour, sugar, vanilla and egg. When the milk in the pot is hot, add the milk and egg mixture into the pot, whisking quickly so that everything incorporates. Cook over medium heat until thickened (4-5 minutes).
Remove from the heat until ready to serve (it will stay warm, and can easily be reheated over low if needed. Whisk periodically to prevent a skin from forming).
Pancakes:Combine flour, baking powder and baking soda in a medium bowl. Add egg, vanilla, lemon juice, and milk. Whisk until smooth. Stir in berries.
Grease griddle with non-stick spray or butter and preheat to medium heat. Ladle scoops of batter onto preheated griddle and cook until golden on each side, about 3-4 minutes on the first side and 1-2 minutes on the second side.
Top with warm custard sauce and additional berries if desired.