Cut parchment paper to fit a 8" x 8" pan with extended sides for easy removal. (I used a 7" x 10" pan I had.) Lightly oil bottom and sides. Preheat oven to 350 degrees.
In a stand mixer; add 3 egg yolks and sugar to the bowl fit with the paddle. Mix at medium-high heat for 2 - 3 minutes until light colored and light. Add vanilla, mix in. Sift gluten free flour (or regular flour) with baking powder and salt - add to bowl, mix over low speed until just combined.
Add the chopped dates and walnuts, mix on low speed until just combined. Whip the three egg whites until stiff peaks form, but not dry.
Fold the egg whites into the batter gently, not to deflate the egg whites much until just combined with a rubber spatula. Fold into the baking pan, leveling the top.
HINT: If using gluten free flour - the batter will be stiff. I used my hands to incorporate the egg whites, like you do with meat loaf. May sound strange, but works perfectly!! Using regular flour - a rubber spatula will do fine.
Bake for 30 minutes until the top is golden, and the top feels just firm. Crack open the oven, let stand for 10 minutes. Do not overtake.
Remove to cool on a wire rack. When still slightly warm, remove the bars from the pan, using the ends of the parchment paper. Cool. Cut into 24 even sized bars. Dust the tops with confectioner's sugar when still a little warm.
Store in a container with a good seal, wrapped in waxed paper. These freeze great! Bring to room temperature and enjoy.