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1
Preheat oven to 325 degrees.
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2
Line 2 cookie sheets with parchment paper.
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3
Whisk flour and salt together in a small bowl to aerate and combine; set aside.
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4
Melt the white chocolate in top of double boiler or microwave; stir until smooth.
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5
In a large bowl with an electric mixer on medium-high speed, beat butter until creamy, about 2 minutes.
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6
Add sugar and brown sugar gradually, beating until light and fluffy, about 3 minutes, scraping down the bowl once or twice.
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7
Dissolve the instant powder in the vanilla, then beat into butter mixture.
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8
Beat in melted white chocolate.
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9
Add about one-third of flour mixture and mix on low speed.
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10
Gradually add remaining flour mixture, mixing just until blended.
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11
Stir in chocolate chunks and chopped toffee bars.
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12
(You may freeze dough up to 1 month; defrost in refrigerator overnight before proceeding).
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13
Drop by generously rounded tablespoon 2 inches apart on cookie sheets.
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14
Flatten cookies with palm of hand to about 1/2-inch thickness.
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15
Bake for about 25 minutes or just beginning to turn light golden brown.
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16
The centers will still be a bit soft.
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17
Place sheets on racks to cool cookies for 2 minutes, then remove cookies from sheets and place directly on racks to cool.