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1
Preheat the oven to 350 degrees F. Lightly butter a 9-by-13-inch baking dish; line with parchment paper, leaving an overhang on 2 sides.
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2
Butter the parchment.
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3
Whisk the flour, oats, malted milk powder, cardamom, ginger, cinnamon, cloves and salt in a large bowl.
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4
Beat the butter and brown sugar in a large bowl with a mixer on medium-high speed until light and fluffy, 3 to 5 minutes.
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5
Add the egg and vanilla and beat until combined.
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6
Reduce the mixer speed to low; beat in the flour mixture until just incorporated.
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7
Transfer the batter to the prepared pan and spread evenly.
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8
Bake until the top is golden brown and the edges start to pull away from the sides of the pan, 20 to 25 minutes.
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9
Remove from the oven and sprinkle with the white chocolate, then return to the oven until the chocolate softens, about 45 seconds.
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10
Remove from the oven and spread the chocolate into a smooth layer.
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11
Top with nonpareils.
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12
Transfer to a rack and let cool completely, then lift out of the pan using the parchment; cut into squares.
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13
Photograph by Andrew Purcell
