Pre-heat oven to 350 degrees F and plug in waffle iron.
In a stand mixer, cream sugars and butter until fluffy. Add eggs one at a time. In a glass, mix buttermilk and vanilla. In a third bowl, mix dry ingredients, flour, salt and baking soda. Alternate mixing dry ingredients and milk mixture into your batter. Lastly, add food coloring until batter is a golden Eggo yellow.
The next step will depend on how hot your griddle is. Mine ran very hot and was vintage, so it didn't have an adjustment setting, so my cook time had to be very short. I placed a heaping half cup of the batter onto my greased waffle iron and cooked for thirty seconds (any longer and it would brown too much and lose the Eggo coloring I was going for). After all of my cookies were pressed, I placed them on several baking sheets and baked in the oven for ten minutes each.
For Buttercream Butter Pat:
In a stand mixer, beat room temp butter until fluffy. Add icing sugar one cup at a time. Add whipping cream, salt and desired color (enough yellow food coloring to turn the frosting to a butter-yellow) and whip until very pale and airy. Scoop into a butter-shaped mold created with cardboard and tape, then lined with parchment and chill in freezer until hard. Remove from mold and slice into 1/8-inch thick slices and use heart-shaped cut-out to create your butter pats. This can be done separately and frozen until ready to apply.
Mix all ingredients in a microwave safe bowl. If mixture is too thick or grainy, heat in microwave at 15 second intervals until desired syrup consistency is reached. Place in piping bag with 1/8-inch circular opening and drizzle over waffle cookies in a continuing 'S' pattern.