Line 2 to 3 large baking sheets with parchment paper or use silicone mats.
Place the softened butter and sugar into a mixing bowl (you can use stand mixer or hand mixer for this recipe). Beat the butter and sugar together on high speed until the butter is light in color and fluffy, about 3 to 4 minutes. Next, add in the egg and vanilla extract and mix again on medium speed for 1 to 2 minutes, until the egg is well beaten.
In a separate bowl, combine the dry ingredients: flour, baking powder and salt and stir to combine. Add the dry ingredients into the cookie batter and mix on low speed for a couple minutes until a cookie dough begins to pull into a ball. If needed, use your hands to gently knead the dough together.
Divide the dough in half and lightly flour your work surface and rolling pin. Roll the dough out gently until it is ¼-inch/6-mm thick. Turn the dough over a few times to keep it from sticking to the surface. Use a heart shaped cookie cutter to cut out small or large hearts. Next, transfer the cookies onto lined baking sheet, spacing them apart about 1 ½-inches/3 ½-cm. Collect the dough scrapes and reuse them.
Method 2: Alternatively, wrap the prepared cookie dough tightly in plastic wrap and refrigerate for at least 1 hour, or overnight. When ready to make the cookies, roll out the dough on a lightly floured work surface. Handle the dough as least as possible with your hands, as the warmth will cause the dough to soften too much.
Place the baking sheets with the prepared cookies into the refrigerator for at least 45 minutes to one hour. Start preheating your oven to 350F/177C. Once the cookies are chilled, remove 1 baking sheet at a time and place it directly into the preheated oven. Bake for 11 to 12 minutes, just until the bottoms of the cookies are slightly golden; the tops should stay pale white.
Allow the cookies to cool on the baking sheet for 10 minutes, then transfer them onto a wire rack to cool completely.
While the cookies are baking and cooling, prepare a batch of my ‘Raspberry Buttercream’, instructions below.
For my decorating method, I transferred the frosting into a pastry bag tipped with a small, round tip; I used Wilton #12. Pipe the frosting onto the cookies in a heart shape and then smooth with an off-set spatula. Alternatively, simply use an off-set spatula to spread the frosting onto the cookies.
Cookies can be enjoyed immediately. Since this frosting is made with real butter, I recommend keeping the cookies stored in the refrigerator, if you don’t plan to eat them all the same day. Store them in an airtight container in the fridge for up to 1 week and remove them about 30 minutes to an hour before enjoying, to allow the cookies and buttercream to soften.
Prepare the raspberry sauce first. Place the raspberries and granulated sugar into a small saucepan and bring the berries to a simmer over medium heat. Simmer for 4 to 5 minutes, until the berries start to fall apart and form a jam. Pour the jam into a fine mesh strainer arranged over a mixing bowl. Use the back of a spoon or a spatula to press the sauce through the strainer, leaving the seeds behind. Discard the seeds and place the sauce into the refrigerator to chill.
Next, prepare the buttercream. The butter needs to be just slightly softened, not melted. If the butter is too soft, return it to the refrigerate to chill. Place the softened butter into a mixer bowl and whisk on high speed for 7 to 10 minutes, until the butter is fluffy, creamy, and pale white in color. Make sure to scrap down the sides of the mixing bowl often to ensure all the butter is well-mixed.
Add the confectioner’s sugar next and start mixing on low speed first until the sugar is incorporated. Once all the lose sugar is incorporated, turn the mixer to high speed and whisk for 3 to 4 minutes, until the buttercream is light and fluffy. Scrap down the sides of the mixing bowl periodically to make sure everything is well mixed.
If desired, add a few drops of red food coloring at this time. For a sourer buttercream, add the citric acid. For even more raspberry flavor, add raspberry extract. Add the chilled raspberry sauce last! Add the sauce and mix for about 15 to 20 seconds, 30 seconds maximum, with the mixer. Do not overmix or this will cause the buttercream to separate! Finish mixing in the sauce by hand using a spatula and use.