Well, the trick is to have the right recipe.
Where do you live? Where I live it was almost impossible to find unsweetened baking chocolate, and i had to use a recipe that used cocoa. But the recipe has to have lots of sugar, lots of butter, and no milk.
You melt the butter (and if you have unsweetened chocolate, you melt the butter with the chocolate - with cocoa, you mix the cocoa with the flour)
You add the sugar. Mix it up but don;t need to beat. Add eggs one at a time, and mix by hand, without beating (you don;t want to add air, you want chewy and dense).
Then add the dry ingredients, just mix to combine and pour into pan.
Make sure you don't overcook.
I'm sure there are plenty of recipes, but here's the one i found using cocoa:
grease a 15 inch by 10 inch by 1 inch pan
250 grams butter (1 1/4 cup)
2 1/2 cups sugar
5 eggs
1 1/4 cups flour
2/3 cups cocoa (unsweetened)
1 tsp baking powder
1 tsp salt
you can also do thick brownies in a 13 inch by 9 inch by 2 inch cake pan
then use:
3/4 cup (150 grams) butter
1 1/2 cup sugar
3 eggs
3/4 cup flour
1/2 cup cocoa (unsweetened)
1/2 tsp baking powder
1/2 tsp salt
Melt butter, add sugar, stir, stir in eggs one at a time, mix or sift dry ingredients and mix in. pour into pan and bake -
350 degrees F (175 C)
i don't remember the times, i just keep checking them after about 25 min.
good luck.
(no doubt there are better recipes than this one, but it's pretty chewy)