These are crispy on the outside, soft in the middle and joyfully colorful throughout.
Preheat the oven to 350 degrees F/180 C. Line 2 baking sheets with parchment paper.
Toast about half of the coconut on an ungreased cookie sheet at 350 degrees F/180 C for about 8-10 minutes, tossing frequently until light brown. Then mix that half with the untoasted coconut. For a crunchier macaroon, pulse some or all of the coconut in a food processor to chop it and achieve an almost shredded texture.
Mix the coconut, sweetened condensed milk and vanilla together in the large bowl until well combined. Set aside.
Separate the eggs and beat the whites and the salt, preferably in a stand mixer, at low speed. Once they have begun to foam, raise the mixer speed slowly and beat until the whites form stiff peaks. Be patient, as the process may take longer than 10 minutes. Although you can go to a faster speed as the eggs begin to whip, do not go to the maximum speed even though it would hasten the whipping. A slower, steadier process results in stiff peaks that are more stable.
Once the egg whites are in stiff peaks, fold them into the coconut batter in 3-4 batches, as gently as possible. The batter will loosen the more egg whites you add. The goal is to keep the egg whites from deflating while mixing them into the coconut batter.
After the egg whites are fully incorporated, gently fold in 1/4 cup of the sprinkles.
Using a medium-small scoop or 2 tablespoons, drop a clump of the batter onto the cookie sheet. If you want the macaroons to be more regular looking, dip your hands in ice water and gently roll the clump into a ball. After you form all of the macaroons (spaced about 1-2 inches apart), add the remainder of the sprinkles on top, gently pressing them into the macaroons so they do not fall off.
Bake for about 25 minutes or until golden brown around the edges, rotating the baking sheets front to back and switching them on the shelves in the oven. Cool the macaroons on the baking sheet, then put them on a wire rack.
Melt the chocolate in a double boiler or slowly in the microwave. (See note about microwaving.) Once the chocolate is completely melted, spread it over the bottom of each macaroon with a knife, then let the chocolate dry by putting the macaroons on their sides. You could dip the macaroon bottoms in the chocolate, but I find that too messy and also it gets a thicker layer of chocolate on the bottom, requiring more than 3 ounces to do a batch. The best knife to use is a small offset knife, which is what professionals and serious bakers use for frosting cakes, but a butter knife works fine. Once the bottoms are dry, if desired, drizzle a few threads of melted chocolate over the top.
Substituting unsweetened coconut for sweetened - If you prefer, or only have access to unsweetened coconut, you can use this technique to sweeten it and substitute it in this recipe.
Fluid ounces vs. ounces by weight - The 14 ounces listed on the can of sweetened condensed milk is a measure of weight. It does not equate to 14 fluid ounces, which is a volume measurement. There are about 10 fluid ounces in a can of sweetened condensed milk, so this recipe calls for half a can.