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Preheat oven to 325 degrees F.
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Line 2 heavy baking sheets with parchment paper.
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Finely chop the oats in a food processor.
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Transfer the oats to a medium bowl.
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Mix in the flour, baking powder, baking soda, and salt. Set aside.
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Using an electric mixer, beat the butter and sugars in a large bowl until fluffy.
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Beat in the eggs and vanilla.
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Add the flour mixture and stir just until blended.
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Stir in the toffee, hazelnuts, and chocolate chips.
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For each cookie, drop 1 rounded tablespoonful of dough onto sheet, spacing 1 inch apart (do not flatten dough).
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Bake until the cookies are golden (cookies will flatten slightly), about 15 minutes.
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Cool the cookies on the baking sheets for 5 minutes.
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Transfer to a cooling rack and cool completely. (The cookies can be prepared 1 day ahead. Store in an airtight container at room temperature.)