<xsl:stylesheet version="2.0"
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
     xmlns:rcp="http://www.brics.dk/ixwt/recipes">

  <xsl:template match="/">
    <xsl:for-each select="doc('recipes.xml')//rcp:recipe">
      <xsl:variable name="r" select="."/>
      <xsl:for-each select=".//rcp:ingredient/@name">
      <xsl:variable name="i" select="."/>
        <xsl:for-each select="doc('fridge.xml')//stuff[text()=$i]">
          <xsl:value-of select="$r/rcp:title/text()"/>
        </xsl:for-each>
      </xsl:for-each>
    </xsl:for-each>
  </xsl:template>

</xsl:stylesheet>