Combine flour, pecans, sugar, baking powder, baking soda, and ½ teaspoon salt in a large bowl. Whisk together milk, sour cream, and 1 egg in a separate bowl. Stir milk mixture into flour mixture until just blended and smooth.
Heat a griddle or large nonstick skillet over medium heat; butter. Pour about ¼ cup batter for each pancake onto griddle. Cook until tops are covered with bubbles and edges look dry, 3 to 4 minutes. Turn and cook until plump and cooked through, 3 to 4 minutes. Repeat with remaining batter.
Slice each pancake in half and arrange, flat side down, in two snug rows in an 8-by-8-inch baking dish. Scatter half of the blueberries over the pancakes, tucking a few in between. Whisk together half-and-half, sugar, vanilla, cinnamon, remaining 4 eggs, and remaining ½ teaspoon salt in a bowl. Pour egg mixture over pancakes. Chill at least 4 hours and up to overnight.
Preheat oven to 350°. Bake until puffed and set, 35 to 40 minutes. Let stand 10 minutes.
Sprinkle with remaining blueberries and drizzle with Honey Sour Cream. Serve warm.
Honey Sour Cream
Whisk together sour cream, half-and-half, honey, lemon zest, and a pinch ofsalt until smooth. Makes 1/2 cup.
To fill an 8x8-inch dish snugly, you will need to make 12 pancakes to cut in half.