Let the eggs and butter sit outside the refrigerator for at least 30 minutes (or longer). Grease or line with parchment paper a 8x12inch baking pan.
Preheat the oven to 350° F (175° C). In a large bowl, add the eggs and sugar. Beat until smooth and fluffy.
Add the vanilla and almond extract, and butter cut in pieces and mix again, until mostly smooth.
Add the all-purpose and almond flour, salt and baking powder. Mix until combined (don't over mix!).
Fold in one cup of blueberries (save the other cup for the top).
Pour the batter in the pan and flatten it out. Top with the remaining blueberries (press them into the batter with your fingers or a spoon). Sprinkle with sliced almonds. And cake for 30 to 40 minutes at 350° F (175° C) until slightly golden on top. Test with a toothpick for readiness. The toothpick should come out clean ... unless of course you poke a blueberry :) Let the cake cool down for a few minutes before cutting in squares.
