Preheat oven to 325°F (160°C). On the stove, set a metal bowl over a pot of simmering water (or use a double-boiler) and add 1/2 cup (125 mL) butter and the sugar and chocolate. Stir a few times as butter and chocolate melt.
Meanwhile, dissolve 1 1/2 tsp (7 mL) instant coffee in 2 tbsp (30 mL) hot water. Add to butter and chocolate, mixing until smooth. Remove chocolate mixture from heat and cool until barely warm before whisking in eggs and 1 tsp (5 mL) vanilla.
In another bowl, mix flour and salt. Whisk into chocolate mixture until smooth. Spread in a greased 8 x 8-in. (20 x 20 cm) baking pan. Bake in centre of oven, 25 min., or until top is just set.
To make the icing, combine remaining butter, icing sugar and cocoa powder in a small bowl. Mix in remaining instant coffee and vanilla and 1 tbsp (15 mL) hot water, stirring until smooth. Ice brownies in their pan while still hot. When cool, cut into 20 pieces to serve.