There are not specific Handbooks devoted to Spanish Constitutional Law writen in English. Some resources of information are avaliable on the Internet. Be careful with those materials. For example, you can download an updated version of the Spanish Constitution at https://www.boe.es/legislacion/documentos/ConstitucionINGLES.pdf (provided by the Official State Gazette -Boletín Oficial del Estado-), which includes the ultimate version of Art. 135 after the last amendment in 2011. Other resources can also help the student to follow theConstitutional debates and the "state of the art" at the moment. See, for example: http://www.iconnectblog.com/2017/11/developments-in-spanish-constitutional-law-the-year-2016-in-review/. The Spanish Constitutional Court (Tribunal Constitucional) web page has also translated into English some of its decisions in leading cases, they are avaliable at https://www.tribunalconstitucional.es/en/jurisprudencia/Paginas/resoluciones-traducidas.aspx

See also:

Lesson 1.Laws, J. (2012). THE GOOD CONSTITUTION. The Cambridge Law Journal, 71(3), 567-582. doi:10.1017/S0008197312000827

Lesson 6 http://www.unirioja.es/dptos/dd/redur/numero1/pascual.pdf

In Spanish, you can also see, among others:

· José Antonio Portero Molina, “Contribución al debate sobre la reforma del Senado”, Revista de Estudios Políticos, n.º 87 (1995), págs. 81-105.

· Javier Ruipérez, La protección constitucional de la autonomía, Tecnos, Madrid, 1993

. Javier Ruipérez, Constitución y Autodeterminación, Tecnos, Madrid, 1995

. Javier Ruipérez, El constitucionalismo democrático en los tiempos de la globalización, UNAM, México, 2005

· Santiago Roura Gómez, Federalismo y Justicia Constitucional. El Tribunal Constitucional y las Comunidades Autónomas, Biblioteca Nueva, Madrid, 2003

- Santiago Roura y Javier Tajadura (Dir.), La reforma constitucional, Bilioteca Nueva, Madrid, 2005.

· Sonia Garcìa Vàzquez, La controvertida reforma de la Ley Orgànica del Tribunal Constitucional, Andavira, A Coruña, 2009.

· Francisco Tomás y Valiente, El reparto competencial en la jurisprudencia del Tribunal Constitucional, Tecnos, Madrid, 1998.