To prepare bread pudding: Place sugar in a saucepan over medium-high heat and cook, stirring occasionally, until the sugar becomes a light golden color. Pour into a 9-inch square ceramic or glass baking dish and tilt the pan to evenly coat the bottom and sides with sugar. Set aside to cool.
Line the pan with bread slices and drizzle butter evenly over the bread. Scatter pineapple and chocolate chips over top.
In a mixing bowl, whisk together eggs, milk, tequila, Kahlúa and vanilla extract. Pour mixture over the bread and let stand at room temperature for 30 minutes, or until the bread has fully absorbed the liquid.
Preheat oven to 350°F Set baking dish in a large roasting pan, filling with enough water to reach one inch up the sides of the dish. Bake until pudding is firm, about 50 minutes to an hour. Remove from oven and place on a cooling rack.
Using a hand-held mixer, whip cream and sugar until stiff peaks form. Cover and refrigerate until ready to serve.
To prepare sauce: Place milk in a saucepan over medium heat. Stir in baking soda and heat until almost boiling. Add one cup of sugar and stir until dissolved. Place remaining sugar in a skillet and melt slowly over low heat, stirring continuously until the sugar is amber colored. Slowly add caramelized sugar to milk mixture, stirring continuously with a whisk. In a small bowl, dissolve cornstarch in cold water, stirring until smooth. Gradually stir cornstarch mixture into milk mixture and cook over low heat at a slow boil until mixture thickens, about 30 minutes. Set aside to cool.
To serve: When pudding has cooled 20 to 30 minutes and is still warm, cut into squares and place in shallow soup bowls. Spoon Cajeta sauce around squares and top with a dollop of whipped cream. Sift confectioners' sugar over each dessert.