In a food processor, blend the peanut butter powder, the almond flour, and the powdered sugar. Pulse to combine. Sift the flour mixture through a kitchen sieve to remove any clumps.
Next, whip the egg whites in a mixer with the whisk attachment on high speed until foamy. Gradually add the granulated sugar and the vanilla extract, continuing to whip until until stiff peaks form.
Fold in half of the flour mixture, gently, with a spatula. Once the first half is mostly incorporated, fold in the remaining flour mixture.
Transfer the batter to a pastry bag with a round-tip if you have one, or add the batter to a plastic food bag and snip off the corner, creating an about ¼-inch hole.
Preheat the oven to 375°F and line two baking sheets with parchment paper.
Holding the bag of batter directly above the baking sheet, pipe circles of batter onto the paper, about 1 ½ inches wide and 1 ½ inches apart.
When all the cookies have been piped (about 30), lift the baking sheets about 3 inches off the counter and drop them. Repeat this twice more to settle any air pockets out of the cookies.
Allow the cookies sit at room temperature to dry slightly, about 15 minutes or until the surface doesn't stick to your finger when lightly touched.
When the cookies have dried slightly, bake them 14 minutes, until just crisped. Allow the cookies to cool before removing from the parchment paper.
To finish the macarons, spread 1 ½ teaspoons jam on one cookie, sandwiching with another cookie, flat sides in. Repeat until all cookies have been used.
Serve, with cold milk if desired.