Split vanilla bean with a paring knife and scrape out seeds with the flat of the blade; reserve seeds for another use. Combine split vanilla pod with goat’s milk, sugar, baking soda, and salt in a 5-quart stainless steel pot. Warm over medium heat, stirring occasionally with a heat-resistant spatula, until sugar dissolves and milk turns foamy and light, about 15 minutes.

Continue cooking at a gentle simmer, stirring and scraping the sides of the pot frequently if not constantly, until milk is thick, golden, and reduced to no more than a thin, super-jammy layer, about 45 minutes; stir more frequently as the cajeta thickens to prevent scorching. Continue cooking until cajeta forms a "trail" that remains open for 1 second when a spatula is scraped across the bottom of the pot. Remove from heat. Using tongs, remove and discard vanilla pod. Scrape cajeta into a heat-resistant, wide-mouth glass jar. If the total amount is less than 12 ½ ounces (1 cup; 355g), thin with a touch of milk or water or else the cajeta will be too thick on cooling. Cajeta can be refrigerated for up to 3 months.