Preheat the oven to 350° F.
Cream together the butter, sugar and brown sugar for 1 minute, until light in color and fluffy in texture.
Scrape the sides of the bowl and add in the eggs and vanilla. Mix until combined.
Add the flour, graham cracker crumbs, baking powder and salt. Mix until a soft dough forms.
Portion the dough out into generous 3 tbsp portions.
Roll into a ball and then smash slightly, so it looks like a hockey puck. The cookies will spread some while baking, so keep it pretty thick.
Bake for 9-11 minutes, or until the cookies have spread and are no longer wet and glossy in the center.
Remove from the oven and allow the cookies to cool on the pan.
Once cooled completely, place the cookies in the fridge to chill while making the topping.
To make the peach buttercream: slowly cream the salted butter until smooth.
Add in 1 cup of powdered sugar at a time, alternating with a little bit of the torani syrup to bring the mixture together.
Once all of the powdered sugar is incorporated into the butter, add another cup of powdered sugar. Repeat this step until all of the powdered sugar and torani syrup is added and mixed in.
Mix thoroughly. At this point, you can add a little heavy cream here to adjust the consistency, if desired. I like to keep mine pretty thick.
To assemble the cookies, spread a generous amount of the peach buttercream onto the chilled cookie.
Top with a dollop of whipped topping, spread to cover the top of the cookie.
Then finish the cookie with a peach slice.
Serve chilled.
Store in the fridge for up to 5 days or they can be frozen for up to 3 months.