Let’s create this vibrant Fruity Pebble Cake:

1. Infuse Buttermilk & Prepare Pans/Oven:

In a small bowl, combine the 1 cup + 1 tbsp buttermilk and ½ cup Fruity Pebbles cereal. Stir and set aside to infuse while you prepare other ingredients (at least 15-30 minutes).

Preheat oven to 350°F (180°C / 175°C fan). Grease three 6-inch round cake pans, line bottoms with parchment paper, and grease/flour the parchment/sides.

2. Prepare Dry & Wet Cake Ingredients:

In a large bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.

In a medium bowl, whisk together the room temperature eggs, vanilla extract, and lemon extract. Set aside. (Self-correction: Original directions combine all wet except buttermilk. Following that).  

Revised Step 2/3:

• (Dry) Whisk flour, baking powder, salt. Set aside.
• (Cream) In stand mixer bowl (paddle attachment), cream room temp butter, oil, and granulated sugar on medium speed until fluffy (3 mins).
• (Wet) Whisk eggs, vanilla, lemon extract. Stream into mixer bowl while mixing on low until combined. Scrape bowl.
• (Infused Buttermilk) Strain the Fruity Pebbles out of the buttermilk, pressing gently on solids; discard soggy cereal. Measure out the infused buttermilk. Combine this with the room temperature sour cream.

3. Combine Cake Batter:

Add about one-third of the dry ingredients to the butter/sugar/egg mixture. Mix on low speed until almost combined.

Add about half of the infused buttermilk/sour cream mixture. Mix on low until almost combined.

Repeat alternating dry and wet ingredients, ending with the dry ingredients. Mix on low just until combined after each addition. Do not overmix. Use a spatula to scrape bottom and ensure no flour pockets remain.

4. Bake the Cake Layers:

Divide batter evenly amongst the three prepared pans (approx. 370g each if weighing). Use an offset spatula to smooth the tops.

Bake for about 26 minutes, or until the tops bounce back when lightly touched and a toothpick inserted into the center comes out clean.

5. Cool the Cakes:

Let cakes cool in the pans on wire cooling racks for 20 minutes.

Run a knife or thin offset spatula around the sides of the pans. Carefully invert the cakes onto the racks, remove parchment, and let cool completely.

6. Make the Cereal Milk:

While cakes cool, make the cereal milk. In a small bowl, combine the 4 tbsp milk and ¼ cup Fruity Pebbles cereal. Let it sit and infuse (at room temp or fridge) for at least 15-20 minutes. Strain out and discard the cereal solids, reserving the flavorful milk.

7. Make the Cereal Cake Crumb:

Reduce oven temperature to 300°F (150°C). Line a baking tray with parchment paper.

Combine the melted butter, flour, sugar, ½ cup Fruity Pebbles, vanilla extract, and baking powder in a bowl. Mix with a spoon until it forms crumbly pieces.

Spread the crumbs out onto the lined baking tray.

Bake for 15 minutes, or until lightly golden and crisp. Set aside to cool completely. Break up any large clumps once cool.

8. Make the Cereal Milk Buttercream:

In a stand mixing bowl (paddle attachment), cream the room temperature butter on medium speed until smooth and lump-free.

Add the sifted powdered sugar and mix on low speed until combined.

Increase speed to high and mix until the buttercream is light and fluffy.

Add 2 tablespoons of the prepared Cereal Milk and mix on medium speed until combined and smooth.

9. Assemble the Cake:

Level the tops of the completely cooled cake layers with a serrated knife.

Use a pastry brush to lightly brush each cut cake top with some of the remaining Cereal Milk.

Place one cake layer on a cake stand or serving plate. Spread an even layer of the Cereal Milk Buttercream over the top.

Sprinkle about ¼ cup of the prepared Cereal Cake Crumb evenly over the frosting.

Place the second cake layer on top. Repeat brushing with Cereal Milk, spreading buttercream, and sprinkling with ¼ cup Cereal Cake Crumb.

Place the final cake layer on top, upside down for a flat surface. Brush this layer with Cereal Milk as well.

10. Frost and Decorate:

Apply a thin crumb coat of the buttercream over the entire cake. Chill for 15-20 minutes.

Use the rest of the buttercream to frost the entire cake smoothly. (Note: Recipe mentions this might only be enough for a thin layer and suggests doubling for thicker frosting).

Gently press more of the Cereal Cake Crumbs onto the top of the cake (or around the base, or both!).

Serve and enjoy! Store leftovers covered in the refrigerator