Grind Fruity PEBBLES™ cereal to a fine dust in a high-powered blender, food processor or by hand using a rolling pin and a freezer bag (must finely strain if doing by hand to eliminate any large pieces).
Combine ½ cup PEBBLES™ and 1 ½ cups heavy whipping cream in a medium bowl then place in the refrigerator to chill until the flavor is infused, about an hour or more. The color will not bleed but the flavor will.
Then weigh all ingredients with the kitchen scale and set aside, ensuring that you remember which egg whites are 90 and which are 82.
Line baking sheets with silicone mats or parchment paper and fit piping bag with the round tip. Place prepped piping bag in a large glass to hold it upright.
Combine powdered sugar and almond flour in a food processor and pulse until very fine, about 15 times.
Pour into a large bowl, whisk in fruity PEBBLES™ powder then sift together to mix and remove any remaining lumps.
Pour dry ingredients into a large bowl and make a well in the center. Carefully pour the 82 grams of egg whites into the center. Fold until well blended into a thick paste and set aside.
Gently heat granulated sugar and water in a small saucepan over medium heat fitted with a candy thermometer and place a stand mixer fitted with the whisk attachment, or in a large mixing bowl using an electric mixer, nearby.
Once the temperature reaches 200 degrees place the 90 grams of egg whites in the stand mixer and whisk on medium speed until soft peaks form (when beaters are lifted out of the bowl the tip of the meringue flops over slightly). Then turn to low speed only to keep the whites moving and prevent them from separating while continuing to heat syrup to 248 degrees Fahrenheit.
As soon as syrup reaches 248 degrees remove from heat and increase mixer speed to medium and carefully pouring the syrup down the side of the mixing bowl until thoroughly combined. Then increase the speed to medium high and whisk sugar and egg whites together until glossy and stiff peaks form (will stand straight up without flopping over when beaters are lifted)
Once your Italian meringue has reached stiff peaks, gently fold into the almond/powdered sugar paste in thirds, until completely smooth and thick ribbons run off your spatula.
Transfer batter to prepped piping bag. Holding the piping bag directly above the prepped baking sheet, pipe 1" rounds about 1" apart. Once all the rounds are piped, sprinkle a stripe of crushed PEBBLES™ down the side of half of the circles, leaving half unadorned. Give the sheet a couple good whacks on the counter to help release any air bubbles, then allow them to rest at room temperature until a skin has formed. This depends on the humidity of your kitchen and how large your cookies are among other factors, but it's usually around 15-30 minutes. You know they're ready when you can touch them and no batter sticks to your finger.
Once the skin has formed, place macarons in the middle rack of the oven, reduce heat to 325 degrees, and bake for 10-12 minutes.
Remove from oven and cool on baking sheet 3-5 minutes before transferring to a cooling rack.
Repeat for remaining macarons, increasing oven back to 350 degrees before baking each batch, then again reducing to 325.
Meanwhile, make cereal milk cream. Place a couple teaspoons of cool water in a small bowl and sprinkle gelatin over. Allow to dissolve then heat until clear and set aside to cool. Strain cereal from heavy cream using a fine mesh strainer and pressing down on the solids to remove as much of the liquid as possible. Add additional cream to bring the total amount of liquid to 1 cup total then place in mixing bowl. Add powdered sugar and whip the mixture until it starts to thicken and soft peaks form, then turn the mixer to low speed. Slowly pour in the gelatin mixture until well combined. Increase the mixer to medium speed and continue mixing until stiff peaks form.
Once completely cool and ready to assemble, flip over the half of the shells that do not have a PEBBLES stripe and pipe a generous round of cereal milk cream around their edges. Sprinkle the space in the center with whole Fruity PEBBLES and top with one of the shells with a PEBBLES stripe.
Filling will maintain its shape at room temperature for a couple of hours, but it’s best to keep the filled macarons refrigerated. Store Fruity PEBBLES Cereal Milk Macarons in an airtight container at room temperature for a day, refrigerated for up to 7 days or freeze for up to 6 months.