Start by making the dough for the cookies. Place the flour, baking powder and salt in a bowl and mix together with a whisk and set aside.
Using an electric stand mixer with the paddle attachment, whip the softened room temperature butter, the lemon zest and the granulated sugar on medium speed until the mixture is light and fluffy, being sure to scrape down the sides occasionally. Add the ricotta and vanilla extract to the mixture and mix. Then add the eggs to the mixture one at a time and mix.
Add the flour mixture to the ricotta mixture and set to a low speed and let mix for a very brief period, just until combined. Remove the bowl from the stand mixer, cover with plastic wrap and put in the fridge to chill for 2 hours.
For the glaze frosting, in a mixing bowl, add the melted butter, powdered sugar, lemon juice, vanilla and milk and whisk until smooth. If the frosting is too thick, add more milk 1 teaspoon at a time and stir, until you get the right consistency, which is thinner than a cake frosting but thicker than a doughnut frosting. If it is too thick, you can add more powdered sugar a tablespoon at a time. Set in a cool place or in the fridge until you are ready to use it.
After an hour and forty minutes of chilling the dough, preheat oven to 350° F degrees. Line several baking sheets with parchment paper.
Scoop out one spoonful of chilled dough, shape it into a ball with your hands and place it on the lined baking sheet (ungreased cookie sheet). Form ricotta cookie dough balls until you have used all the remaining dough, spacing the balls 2 cm from each other on the sheet.
Put the cookies in a preheated oven to bake for approximately 12 minutes, or until the bottoms are lightly golden brown. Remove and let cool on the baking sheet for several minutes until the soft cookies get a little firmer on the outside and then set cookies on a wire rack to cool completely.
Once the cookies are cool, remove the frosting glaze from the fridge and let it come up to room temperature, stirring until smooth and slightly runny. If it has hardened too much, you can add a tsp of milk and stir well.
Take a spoonful of icing and drizzle over the top of each cookie. Add sprinkles immediately if you are using them so that they harden into the glaze. Leave the cookies at room temperature until the icing has set and then serve.