Preheat oven to 350°. Line a 9″x 13″baking pan with foil and butter the foil.
Stir together flour, baking powder, and salt. Set aside.
Using a heavy-duty mixer on medium speed, beat butter and sugar until soft and light (about 5 minutes). Add whole eggs, one at a time, beating well after each addition. Beat in vanilla.
On low speed, add half the flour mixture and mix well. Add yolks, mixing well, then add remaining flour mixture.
Scrape batter into prepared pan. Smooth the top. Scatter blueberries over the batter.
Combine flour, sugar, cinnamon, and nutmeg. Stir in melted butter and combine with your fingers until the mixture is coarse crumbs. Scatter the crumbs evenly over the berries.
Bake for 40 minutes, or until cake is firm. Cool cake in pan on wire rack.