Preheat oven to 375 degrees.

In a small bowl, combine flour, baking soda, and salt; set aside.

In a large bowl, cream butter and sugars until light and creamy. Beat in egg and vanilla until smooth. Gradually add flour mixture until combined. Stir in orange zest and chips.

Drop rounded teaspoonfuls onto parchment lined cookie sheets. Do not flatten cookies; it will make them dry.

Bake 8 to10 minutes or until golden brown around edges. Do not overcook! Cookies will be plump. Cool for several minutes on cookie sheets before transferring to rack to cool completely. Store in airtight container.

In a food processor, pulse flour, confectioners' sugar, salt, and lemon zest until combined. Add butter and process until sandy. Add egg yolks and lemon juice, pulse until dough comes together.

Divide dough in half and form each into a 1-1/2 inch-wide log. Wrap in plastic and freeze until firm, about 2 hours.

Preheat oven to 350 degrees, with racks in upper and lower thirds. Spread granulated sugar on a piece of parchment, roll logs over sugar to coat. Slice logs into 1/4 inch thick slices and arrange, 1 inch apart, on two parchment lined baking sheets.

Bake until cookies are golden brown around edges, about 15 minutes, rotating sheets halfway through. Transfer cookies to wire racks to cool. To store, cover and keep at room temperature, up to 5 days.

COOKIES: In the bowl of a stand mixer with the flat beater attached, cream the butter and granulated sugar at medium speed until light and fluffy, about 3 minutes. Scrape down the sides of the bowl with a rubber spatula as needed. Add the eggs, one at a time beating until each is incorporated. Add the vanilla and sour cream and beat at low speed until combined.

Add the dry ingredients and beat at low speed until just combined, scraping down the bowl as needed. Dough will be sticky. Divide dough into two sections. Flatten into rectangles about 1 1/2 inches thick, then wrap with plastic wrap. Chill in the refrigerator overnight or at least two hours until firm.

Preheat the oven to 425 degrees. Line 2 large baking sheets with parchment paper, set aside.

Use the plastic wrap that you chilled the dough in. Dust the top of the dough and then flip and flour the other side, keeping it on the plastic wrap. With a rolling pin, roll the dough out to 1/4-inch thickness. Using a 2 1/2-inch round cookie cutter, cut out circles and transfer to a baking sheet. Bake for 7 minutes, until pale golden. Immediately transfer cookies to a wire rack to cool.

FROSTING: In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and vanilla. Slowly beat in the confectioners' sugar. Once smooth and creamy, add in heavy cream, 1 tablespoon at a time until the desired spreading consistency is achieved. If desired, add food coloring and beat until combined. Once cookies have cooled completely, frost and add sprinkles. Allow frosting to set, then store in an air-tight container.