Preheat oven to 350°F. Line two baking sheets with parchment paper. Use cookie racks for cooling and icing, and lay wax paper under each one to catch drips of icing.

Place butter and cream cheese in a large mixing bowl. Use an electric mixer to beat together until blended. Add the sugar and beat a couple of minutes, until light and fluffy. Beat in non-dairy milk, lemon extract, vanilla, and lemon zest.

Add the flour and sprinkle baking powder on top. Without over-mixing, beat until flour is incorporated and a thick dough is formed.

Using a small portion scoop or teaspoon, drop the cookie dough onto the prepared baking sheets. Flatten slightly with the bottom of a glass or measuring cup. Bake for 10 to 12 minutes, until bottoms are lightly browned.

Remove from oven and transfer to racks to cool.

To make the lemon icing, mix together in a small bowl the powdered sugar, lemon juice, and lemon zest. Stir until well blended. Use a spoon to ice the entire cookie, or drizzle icing over several cookies at a time. Decorate with colored sugar, sprinkles, or nonpareils, if desired. Store covered, in layers separated by parchment or wax paper for up to a week.