Step 1

Combine the water, feta, salt, and pepper in a blender and blend until smooth.

Step 2

Place the chicken breasts in a resealable plastic bag or container large enough to submerge the meat. Pour the brine over the chicken, cover, and refrigerate at least 8 hours or overnight.

Step 3

Arrange a rack in the middle of the oven and heat to 400°F. Meanwhile, remove the chicken breasts from the brine, pat dry with paper towels, and place in a single layer in a baking dish or on an aluminum foil-lined rimmed baking sheet. Let sit for about 30 minutes at room temperature.

Step 4

If you'd like, break off a few cloves of garlic from the head, peel, smash, and scatter around the chicken. Cut the top off the remaining garlic head to expose the cloves, cut in half horizontally, then place the 2 pieces in the pan. Sprinkle the rosemary sprigs over the chicken, then drizzle with the oil.

Step 5

Roast until an instant-read thermometer inserted in the thickest part of the breasts reads 165°F, 35 to 45 minutes.

Step 6

Remove the chicken breasts from the oven, squeeze the juice from the lemon half over the chicken, and let rest for 5 minutes before serving. Squeeze the roasted garlic cloves out of their peels onto crostini, if desired.