Baking for a crowd? Sarah Kieffer offers tips and a winning dessert recipe.

"And what is so rare as a day in June? Then, if ever, come perfect days," James Russell Lowell wrote, and I must agree. This summer month is almost faultless.

Extra-long days filled with sitting on patios and glorious sunsets, and those three sweet words my children can't wait to hear: School is out. June, of course, is filled with many opportunities to bake up a storm with graduations, open houses, grill-outs, potlucks, swim parties and summer solstice celebrations. However, feeding the multitudes can often seem overwhelming. Here are my tips for large group baking:

First of all, there are recipes that double well, but not all recipes double well. Cookies are great for doubling, which is convenient because they are also the easiest to make. When I am increasing the volume for cookies, I normally double or triple the recipe as written. Occasionally I will use a little less salt and vanilla, and then taste the dough at the end to see if it needs more of either.

Second, pan size is a crucial variable when doubling. While cookies are portioned and bake up as individual units, things like cakes and brownies need a specific amount of batter poured into a specific-sized pan. So, if you do double these types of recipes, you should still bake the batter in the pan sized called for, which means you would need two pans instead of one when doubling the recipe.

Third, if I am trying out a new recipe for a large group of people, I will do a test run, experimenting on family, friends or neighbors who are OK with less than perfect results. I keep a notebook of my successes and failures, so I remember for the next big event.

Lastly, if you don't have time or resources to experiment, I suggest making two separate batches of the recipe instead of doubling, to ensure success.

When I am feeding a crowd, I love to bake in my half-sheet pans, because I can cut bars into almost 50 servings that way. I've included a recipe here for Chocolate Oat Bars, a variation from my cookbook "100 Cookies." This recipe didn't work to straight-up double; there was too much crust and filling for the half-sheet pan. I have tweaked and fiddled with it to make fit just right so you can enjoy these fudgy bars at your next big event.

Chocolate Oat Bars (for a crowd)

Makes 24 large or 48 small bars.

These bars are similar to old-school oatmeal fudge bars, except the filling here contains sweetened condensed milk, which makes for a smooth, rich center. They are creamy and delicious, with a firm base that gives just enough crunch to complement the filling. The bars will need time to chill before serving. From Sarah Kieffer.

For the chocolate filling:

• 3 (14-oz.) cans sweetened condensed milk

• 12 oz. (340 g) semisweet chocolate, melted

• 3 tbsp. heavy cream

• 1 tsp. pure vanilla extract

• 3/4 tsp. salt

For the oat crust:

• 3 c. (426 g) all-purpose flour

• 2 c. (160 g) quick oats

• 3/4 c. (150 g) brown sugar

• 1/3 c. (65 g) granulated sugar

• 3/4 tsp. baking soda

• 3/4 tsp. salt

• 1 1/2 c. (3 sticks or 339 g) unsalted butter, at room temperature

Directions

Adjust an oven rack to the middle of the oven. Preheat the oven to 350 degrees. Grease a half-sheet pan (17-by-12-by-1 inches).

For the filling: In a large bowl, whisk together the sweetened condensed milk, melted chocolate, heavy cream, vanilla and salt until smooth. Set aside.

For the crust: In the bowl of a stand mixer fitted with a paddle, mix the flour, oats, brown and granulated sugars, baking soda and salt on low speed to combine. Add the butter and mix until the mixture is crumbly.

To assemble: Press a little more than half of the crust mixture into the bottom of the prepared pan and bake for 10 minutes. Remove the pan from the oven and carefully spread the chocolate filling over the hot crust. Sprinkle the remaining crust mixture evenly over the top. Bake for 15 to 20 minutes, until the sides have puffed up slightly and the filling does not jiggle when gently shaken.

Transfer the pan to a wire rack and let cool. Place the pan in the refrigerator and chill for 6 hours. Slice the bars and serve. The bars can be served cold at room temperature but keep best in an airtight container in the refrigerator for up to 3 days.

Sarah Kieffer is a Minnesota baker, cookbook author and creator of the Vanilla Bean Blog. Follow her on Instagram at @sarah_kieffer.