Combine first 4 ingredients in a medium bowl. Beat butter at medium speed with an electric mixer until creamy; add water and next 4 ingredients, beating until combined. Add flour mixture, mixing until just blended. Divide batter equally among buttered jars; wipe rims. Each jar should be slightly less than half full. Place jars on a jelly-roll pan in center of oven; bake, uncovered, at 325° for 40 minutes. Wipe rims; cover with metal lids and screw on bands. Set aside to cool.
TIP: Give Brownies Baked in a Jar with whimsical sundae dishes, colorful spoons and a sampling of ice-cream toppings...a treat to beat the summer heat!