Brownie disaster

Just made brownies, and they’re a disaster. I followed the recipe (taken from here, see Just Desserts) exactly, as it was one I’d not used before, double checking measures . I have a temperature checker, so the oven was ok, and I baked it for the time suggested. When I tested it, it was liquid in the center, so i gave it another 5 mins. Still liquid, so another 5 mins. I finally decided to take it out and it’s like a cookie, not even 1" high. Here’s the recipe, can anyone see anything wrong with it, please?

Restaurant Brownies

3/4 cup (1 1/2 sticks) butter
3 (1 ounce squares) unsweetened chocolate
1 1/2 cups granulated sugar
1 teaspoon vanilla extract
3 large eggs
3/4 cup flour
1/4 teaspoon salt
Frosting (see recipe)

Preheat oven to 350 degrees F. Coat 8-inch pan with vegetable oil spray or butter lightly.
Melt butter and chocolate over low heat, stirring until smooth. Cool, stir in sugar and vanilla. Add eggs, one at a time, whisking until smooth. Stir in flour and salt.
Pour into prepared pan. Bake in preheated oven 25 to 35 minutes or until top is crusty and cake tester comes out clean when inserted near center.
Remove from oven and cool. When cool, frost, then cut into bars.
Makes 24 servings.

2 tablespoons butter
2 (1 ounce squares) unsweetened chocolate
1/2 teaspoon vanilla extract
1 cup sifted powdered sugar
2 to 3 tablespoons coffee-flavored liqueur such as
Kahlúa (or other compatible liquor)

Melt butter and chocolate over low heat or in microwave. Blend until smooth. Add vanilla extract and about half of sugar; mix well. Gradually add remaining sugar and liqueur until mixture reaches spreading consistency.