You can make the shells up to 3 days in advance. Keep them in an airtight container at room temperature.
Make shells: Position a rack in center of oven and preheat to 350°F. Coat 24 mini muffin cups with cooking spray. Stir coconut, egg whites and sugar in a bowl until mixture forms a smooth, cohesive mass. Place 1 scant tablespoon in each muffin cup. With lightly moistened fingers, press mixture evenly into bottom and sides of each cup. Bake until bottoms are golden and edges are brown, 11 to 13 minutes. (The surface should feel dry.) Let cool in cups on a wire rack for 10 minutes, then carefully slide a small offset spatula or knife between each shell and cup to pop shells out. Let cool completely on rack.
Just before serving, make filling: Melt chocolate and almond butter in a heatproof bowl set over a saucepan of simmering water, stirring until smooth (don’t let bottom of bowl touch water). Remove from heat and stir occasionally until cooled to room temperature. Divide filling among shells, about 2 teaspoons each, to almost reach rim. When chocolate has firmed a bit, gently press an almond on top of each tassie. Let stand until chocolate sets.
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