In the bowl of a stand mixer, beat butter and sugar together on high speed until fluffy. (Alternatively, use a handheld electric mixer on high speed). Beat in the eggs, vanilla, ricotta and lemon zest.
In a separate bowl, combine the flour, salt and baking powder.
With the mixer on low speed, slowly add the dry ingredients into the ricotta mixture until combined.
Line 2 baking sheets with parchment paper. Drop the cookie dough in heaping spoonfuls onto the baking sheets, leaving 1 inch of space between them. Bake 20 minutes. Transfer cookies to a cooling rack and cool to room temperature.
To make the frosting, whisk all ingredients together in a shallow bowl. Dip the tops of the cooled cookies into the frosting. Set onto a wire rack to let dry.