It is a spice made from drying and grinding unripe, green jalapeño peppers. It has a distinct 'green' or 'grassy' flavour and a medium heat, different from red chilli powders.
No, they have the same heat level, because chipotles *are* jalapeños! Jalapeño powder has a 'grassy' heat, while chipotle powder is made from *smoked* red jalapeños, so it has a deep, smoky heat.
No, it is much milder. Jalapeño powder has a medium heat (2,500-8,000 Scoville Heat Units). Cayenne pepper is significantly hotter, starting at 30,000 SHU.
It's a staple in Tex-Mex and Mexican cooking. Use it in spice rubs, taco seasonings, and chili. It's also perfect for adding a kick to salsas, guacamole, corn bread, or even sprinkling on popcorn and eggs.
For a similar 'green' flavour, Serrano pepper powder is a good (but hotter) substitute. If you only need heat, a small amount of Cayenne will work, but it will lack the grassy, vegetal flavour.
It's very concentrated. A good starting point is 1/2 teaspoon of powder for every 1 medium-sized fresh jalapeño called for in a recipe. You can always add more, so start small.
