Preheat the oven to 375 degrees.
Line your baking sheets with parchment paper or silicone mats and set aside.
In a large bowl, add the flour, sugar, and salt and whisk together.
Next, zest in your lemon and orange. Then grate in your frozen butter.
Using your hands or a pastry cutter, cut in the butter until you get a nice and crumbly consistency. Then with a spatula stir in your sour cream and vanilla.
Using a dough hook on your mixer or a wooden spoon, mix the dough together until everything is mixed together, and it forms a ball around the hook.
Lightly flour your work area. Divide the dough in half. Place one half on the prepared surface and put the bowl with the other half into the fridge so it stays cold.
Roll the dough to roughly 1/8" thickness. Then cut out a 3" x 2" rectangle for the letter. You can use a small paring knife or a pastry wheel.
Then cut out a small heart for each love letter cookie you make. Using your pastry wheel, make the lines in the cookie to resemble an envelope.
Place the cookies on the cookie sheet and top them with either the white granulated sugar or the turbinado sugar. Then bake for 6 to 8 minutes or until the sides and bottom are lightly browned.
Once the cookies are done, remove them from the oven. Let them cool on the cookie sheet for a few minutes.
When they have cooled, decorate the small hearts however you choose and attach them with a dollop of frosting or icing to the cookie.
Enjoy!