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1
Preheat the oven to 425u00b0F. Line a large baking sheet with parchment paper. Whisk together the flour, baking powder, and salt in a large mixing bowl. Add the cold butter and rub it in with your fingertips or cut it into the flour mixture with a pastry cutter. The butter pieces should be the size of small peas and not all uniform. Add almost all the milk to the bowl and stir with a fork until a dough forms. Make sure to stir any dry flour up from the bottom of the bowl. If the dough seems dry, add the remaining milk, a little at a time.
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2
Turn the dough out onto a lightly floured work surface and knead it, very gently, several times, then pat it into a round shape, about 3/4-inch thick. Cut biscuits with a 3-inch cutter (or any other size you choose), pressing straight down as you proceed. Transfer the biscuits to the prepared sheet. Press together the dough scraps and cut additional biscuits, you should get 6 to 9 from this quantity of dough. Brush the tops with a little melted butter, if you like.
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3
Bake the biscuits until they are firm, well-risen, and golden brown, about 12 to 15 minutes. Remove to a rack to cool.
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4
Combine the mayonnaise, garlic paste, and minced olives in a small bowl. Check for seasoning and add salt if necessary. (If you have used commercial mayonnaise, you might want to add a few drops of fresh lemon juice as well.)
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5
To serve: Rinse, core, and slice your tomatoes. Split each biscuit and spread a generous dollop of aioli on the bottom half. Top with several tomato slices and gently replace the top half of the biscuit. Serve immediately. Leftover aioli should be stored, tightly covered, in the refrigerator. Biscuits can be wrapped and stored at room temperature for a day.
