In a large mixing bowl, cream together the butter and granulated sugar until light and fluffy.
Add the orange zest, vanilla extract, and one of the eggs; mix until combined. Add the second egg and mix well.
In a medium mixing bowl, whisk together the flour, baking powder, and salt. Add the dry mixture to the wet mixture and beat with an electric mixer until combined.
Cover the bowl with plastic wrap or a clean kitchen towel and refrigerate the dough for 30 minutes.
Roll the chilled dough into 30 1-inch balls and place on cookie sheets lined with parchment paper leaving at least 1 inch of space between each cookie. Place the cookie sheets in the refrigerator to chill the dough balls for 30-60 minutes before baking.
While the dough balls chill, preheat the oven to 350F degrees.
Bake the cookies for 10 minutes at 350F until set and lightly browned on the bottom. Transfer the cookies to a wire cooling rack to cool completely to room temperature before frosting.
While the cookies cool, pour the powdered sugar and vanilla extract into a small mixing bowl. Add the cream or milk 1 tablespoon at a time, stirring well between each addition, until the frosting reaches the right consistency. You want the frosting to be just thin enough to drizzle, but not so thin that it runs right off the cookies. If the frosting becomes too thin, add more powdered sugar. Stir in the orange zest.
When the cookies are completely cooled, frost the top of each cookie with a teaspoon of frosting, then add the sprinkles.