In a mixing bowl, cream butter and sugar. Add the eggs, one at a time, beating well after each addition. Beat in ricotta and vanilla. Combine flour, salt and baking soda; gradually add to the creamed mixture.
Drop by rounded teaspoons 2 in. apart onto greased baking sheets. Bake at 350 degrees F for 10-12 minutes or until lightly browned. Remove to wire racks to cool.
For frosting: in a mixing bowl, cream butter, sugar and vanilla. Add enough milk until frosting reaches spreading consistency. Frost cooled cookies and immediately decorate with sprinkles.