Snickerdoodles with Peanut Brittle

STEP 1: MAKE THE PEANUT BRITTLE

Line a sheet pan with parchment paper. In a heavy saucepan, combine the granulated sugar, golden syrup, butter and heavy cream. Cook over medium heat, stirring until the sugar dissolves, then stop stirring and boil, swirling the pan now and then so the cream doesn't catch, until a candy thermometer reads 300°F (hard crack). Take the pan off the heat and stir in the unsalted peanuts and the flaky sea salt. Spread thinly on the lined pan and cool for 20 minutes until hard. Chop into small, even shards; you need 3 per cookie.

STEP 2: HEAT THE OVEN

Heat the oven to 375°F with racks in the upper and lower thirds. Line three sheet pans with parchment paper.

STEP 3: MIX THE DRY INGREDIENTS

Whisk together the flour, cream of tartar, baking soda and fine salt, leveling each measuring spoon with a knife so the leavening is exact.

STEP 4: CREAM THE DOUGH

Beat the softened butter with the granulated sugar and light brown sugar for 2 to 3 minutes until pale and fluffy. Beat in the eggs one at a time, then the vanilla extract. Add the dry ingredients on low speed and stop as soon as no flour shows.

STEP 5: SHAPE AND COAT

Mix the coating sugar and ground cinnamon in a shallow bowl. Using a 1½-tablespoon cookie scoop, portion the dough into 32 level balls of about 30 g each. Roll each ball in the cinnamon sugar. Arrange 12 balls on each of two lined sheet pans, 2 inches apart, and keep the remaining 8 on a plate. Chill everything for 15 minutes.

STEP 6: BAKE A TEST COOKIE

Bake 2 of the reserved balls on the third sheet pan for 9 minutes. Cool for 5 minutes, press a brittle shard onto one, and taste for cinnamon, salt and texture: the edge should be crisp and the center chewy. Adjust the bake time for the batch only if needed.

STEP 7: BAKE THE BATCH

Bake the two full sheet pans on the upper and lower racks for 9 to 10 minutes, swapping and rotating them halfway, until the edges are set and the centers are puffed and still soft. Do not wait for color across the top; the centers settle and crinkle as they cool. Place the last 6 balls on the cooled third pan and bake the same way.

STEP 8: ADD THE BRITTLE

Straight from the oven, press 3 brittle shards into each cookie so they stick. Cool on the pan for 5 minutes, then transfer to a wire rack.

STEP 9: DRIZZLE AND SET

Melt the milk chocolate gently in short bursts in the microwave or in a bowl over barely simmering water. Drizzle the same zigzag over every cooled cookie and let the chocolate set before serving 30.