Place chocolate in microsafe dish or measuring cup. Microwave, uncovered, at MEDIUM to MEDIUM HIGH power until chocolate appears soft, approx. 3 minutes. Stir every minute. Do not overheat. (Or chocolate can be melted in top of a double-boiler over very low heat.) Stir until melted. Remove from heat. Stir in condensed milk, butter and vanilla. Blend until butter is mixed with the chocolate. Stir in nuts. Spread mixture into a lightly oiled 20 cm square pan. Cool at room temperature. SWEETENED CONDENSED MILK: Heat water and sugar in medium saucepan until sugar dissolves, approx. 5 minutes. Add butter. Heat mixture until butter melts. Remove from heat. Place instant milk in food processor or blender. Pour water/sugar mixture into processor/blender. Process until well blended. Makes 1 cup of sweetened condensed milk for fudge recipe. No leftovers like when you use the canned sweetened condensed milk.